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One direct approach which is illustrated by several example files is by having different plant equipment operation schemes (and associated plant equipment list) for on peak and off peak period. The example below is from VAVSingleDuctReheat.idf. Availability managers give control signal at plant level and not component level so yes, they may not be useful for the current purpose. The only other approach can think of could be if there are branch pumps with each chiller (or tower) in parallel branch, different branch pump schedules can be specified. But I have not tested this second approach to recommend it.

  Schedule:Compact,
    On Peak,                 !- Name
    Fraction,                !- Schedule Type Limits Name
    Through: 12/31,          !- Field 1
    For: Alldays,            !- Field 2
    Until: 9:00,0.00,        !- Field 3
    Until: 18:00,1.00,       !- Field 5
    Until: 24:00,0.00;       !- Field 7

  Schedule:Compact,
    Off Peak,                !- Name
    Fraction,                !- Schedule Type Limits Name
    Through: 12/31,          !- Field 1
    For: Alldays,            !- Field 2
    Until: 9:00,1.00,        !- Field 3
    Until: 18:00,0.00,       !- Field 5
    Until: 24:00,1.00;       !- Field 7

  PlantEquipmentOperationSchemes,
    CW Loop Operation,       !- Name
    PlantEquipmentOperation:CoolingLoad,  !- Control Scheme 1 Object Type
    Peak Operation,          !- Control Scheme 1 Name
    On Peak,                 !- Control Scheme 1 Schedule Name
    PlantEquipmentOperation:CoolingLoad,  !- Control Scheme 2 Object Type
    Off Peak Operation,      !- Control Scheme 2 Name
    Off Peak;                !- Control Scheme 2 Schedule Name

  PlantEquipmentOperation:CoolingLoad,
    Peak Operation,          !- Name
    0,                       !- Load Range 1 Lower Limit {W}
    70000,                   !- Load Range 1 Upper Limit {W}
    Chiller Plant,           !- Range 1 Equipment List Name
    70000,                   !- Load Range 2 Lower Limit {W}
    245000,                  !- Load Range 2 Upper Limit {W}
    Chiller Plant and Purchased,  !- Range 2 Equipment List Name
    245000,                  !- Load Range 3 Lower Limit {W}
    500000,                  !- Load Range 3 Upper Limit {W}
    Purchased Only;          !- Range 3 Equipment List Name

  PlantEquipmentOperation:CoolingLoad,
    Off Peak Operation,      !- Name
    0,                       !- Load Range 1 Lower Limit {W}
    900000,                  !- Load Range 1 Upper Limit {W}
    All Chillers;            !- Range 1 Equipment List Name

  PlantEquipmentList,
    Chiller Plant,           !- Name
    Chiller:ConstantCOP,     !- Equipment 1 Object Type
    Little Chiller;          !- Equipment 1 Name

  PlantEquipmentList,
    Chiller Plant and Purchased,  !- Name
    Chiller:Electric,        !- Equipment 1 Object Type
    Big Chiller,             !- Equipment 1 Name
    DistrictCooling,         !- Equipment 2 Object Type
    Purchased Cooling;       !- Equipment 2 Name

  PlantEquipmentList,
    Purchased Only,          !- Name
    DistrictCooling,         !- Equipment 1 Object Type
    Purchased Cooling;       !- Equipment 1 Name

  PlantEquipmentList,
    All Chillers,            !- Name
    Chiller:Electric,        !- Equipment 1 Object Type
    Big Chiller,             !- Equipment 1 Name
    Chiller:ConstantCOP,     !- Equipment 2 Object Type
    Little Chiller;          !- Equipment 2 Name

(Note: There are example files which have same control scheme name "Peak Operation" for both 'On Peak' and 'Off Peak' schedule. I am not sure whether this is as intended or a defect in exmaple files. HeatRecoveryElectricChiller.idf, CoolingTower.idf etc. to name a few but I am sure there are more such files.)

One direct approach which is illustrated by several example files is by having different plant equipment operation schemes (and associated plant equipment list) for on peak and off peak period. If others know a better approach, please chime in. The example below is from VAVSingleDuctReheat.idf. Availability managers give control signal at plant level and not component level so yes, they may not be useful for the current purpose. The only other approach can think of could be if there are branch pumps with each chiller (or tower) in parallel branch, different branch pump schedules can be specified. But I have not tested this second approach to recommend it.VAVSingleDuctReheat.idf.

  Schedule:Compact,
    On Peak,                 !- Name
    Fraction,                !- Schedule Type Limits Name
    Through: 12/31,          !- Field 1
    For: Alldays,            !- Field 2
    Until: 9:00,0.00,        !- Field 3
    Until: 18:00,1.00,       !- Field 5
    Until: 24:00,0.00;       !- Field 7

  Schedule:Compact,
    Off Peak,                !- Name
    Fraction,                !- Schedule Type Limits Name
    Through: 12/31,          !- Field 1
    For: Alldays,            !- Field 2
    Until: 9:00,1.00,        !- Field 3
    Until: 18:00,0.00,       !- Field 5
    Until: 24:00,1.00;       !- Field 7

  PlantEquipmentOperationSchemes,
    CW Loop Operation,       !- Name
    PlantEquipmentOperation:CoolingLoad,  !- Control Scheme 1 Object Type
    Peak Operation,          !- Control Scheme 1 Name
    On Peak,                 !- Control Scheme 1 Schedule Name
    PlantEquipmentOperation:CoolingLoad,  !- Control Scheme 2 Object Type
    Off Peak Operation,      !- Control Scheme 2 Name
    Off Peak;                !- Control Scheme 2 Schedule Name

  PlantEquipmentOperation:CoolingLoad,
    Peak Operation,          !- Name
    0,                       !- Load Range 1 Lower Limit {W}
    70000,                   !- Load Range 1 Upper Limit {W}
    Chiller Plant,           !- Range 1 Equipment List Name
    70000,                   !- Load Range 2 Lower Limit {W}
    245000,                  !- Load Range 2 Upper Limit {W}
    Chiller Plant and Purchased,  !- Range 2 Equipment List Name
    245000,                  !- Load Range 3 Lower Limit {W}
    500000,                  !- Load Range 3 Upper Limit {W}
    Purchased Only;          !- Range 3 Equipment List Name

  PlantEquipmentOperation:CoolingLoad,
    Off Peak Operation,      !- Name
    0,                       !- Load Range 1 Lower Limit {W}
    900000,                  !- Load Range 1 Upper Limit {W}
    All Chillers;            !- Range 1 Equipment List Name

  PlantEquipmentList,
    Chiller Plant,           !- Name
    Chiller:ConstantCOP,     !- Equipment 1 Object Type
    Little Chiller;          !- Equipment 1 Name

  PlantEquipmentList,
    Chiller Plant and Purchased,  !- Name
    Chiller:Electric,        !- Equipment 1 Object Type
    Big Chiller,             !- Equipment 1 Name
    DistrictCooling,         !- Equipment 2 Object Type
    Purchased Cooling;       !- Equipment 2 Name

  PlantEquipmentList,
    Purchased Only,          !- Name
    DistrictCooling,         !- Equipment 1 Object Type
    Purchased Cooling;       !- Equipment 1 Name

  PlantEquipmentList,
    All Chillers,            !- Name
    Chiller:Electric,        !- Equipment 1 Object Type
    Big Chiller,             !- Equipment 1 Name
    Chiller:ConstantCOP,     !- Equipment 2 Object Type
    Little Chiller;          !- Equipment 2 Name

(Note: There are example files which have same control scheme name "Peak Operation" for both 'On Peak' and 'Off Peak' schedule. I am not sure whether this is as intended or a defect in exmaple files. HeatRecoveryElectricChiller.idf, CoolingTower.idf etc. to name a few but I am sure there are more such files.)files. Posted another question on UnmetHours which highlights the above issue.)