Time of Peak is not in Timestep increments

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There are two timesteps in EnergyPlus, the Zone timestep (which is the user input) and a System timestep (which is not). See the description here that states:

There is also second type of timestep inside EnergyPlus that is known as the System Timestep. This is a variable-length timestep that governs the driving timestep for HVAC and Plant system modeling. The user cannot directly control the system timestep (except by use of the ConvergenceLimits object). When the HVAC portion of the simulation begins its solution for the current zone timestep, it uses the zone timestep as its maximum length but then can reduce the timestep, as necessary, to improve the solution. The technical details of the approach are explained in the Engineering Documentation under “Integrated Solution Manager”. Users can see the system timestep used if they select the “detailed” frequency option on an HVAC output variable (e.g. Zone Air Temperature). To contrast, the “Zone” variables will only be reported on the zone timestep (e.g. Zone Mean Air Temperature).

And there is engineering documentation for the Variable (System) Timestep here.

In summary, if a zone air temperature changes by > 0.3 $^0C$ or 0.5 $^0F$, EnergyPlus uses a smaller timestep than what's defined by the Timestep object type to iterate over how the HVAC system serving that zone should respond and avoid instability in the resulting zone air temperature. How small that timestep becomes is dynamic, and you can read more information in the Variable Timestep section of the Engineering Reference.

The "Detailed" reporting frequency option of Output:Variable objects would normally report every model timestep, but also add rows to show those portions of the simulation where this smaller timestep is used. Note that this "Detailed" reporting frequency can ONLY be applied to output variables that have an HVAC timestep instead of a Zone timestep. From the Output Details and Examples section for the eplusout.rdd file:

“Zone” variables are calculated and can be reported after each Zone/Heat Balance timestep (ref: TimeSteps in Hour command). “HVAC” variables are calculated and can be reported with each variable HVAC timestep. “Average” variables will be averaged over the time interval being reported whereas “sum” variables are summed over that time interval.

"Zone" vs. "HVAC" meaning the first word you see in the comment for a given output variable in the RDD output file. Example excerpts from the RDD output file, with ** around the key comment words I'm referring to:

Output:Variable,*,Zone Mean Air Humidity Ratio,hourly; !- **Zone** Average [kgWater/kgDryAir]

"Detailed" reporting frequency would always match the model timestep (Zone).

Output:Variable,*,Zone Air Heat Balance Internal Convective Heat Gain Rate,hourly; !- **HVAC** Average [W]

"Detailed" reporting frequency would show the smaller timesteps, if they are used (HVAC).

You can read this post for another reference, as well as see a diagram for this regarding EMS program calling points.