Sensible-Delayed Solar Fenestration Explanation

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Hi fellas! I have room facing the east with big fenestration. I saw the time of peak load for cooling it shows at 16.40 which means sun position already on the west side of my room. I also check to the estimated cooling peak load component and got the fenestration contribution was quite high, it's not sensible-instant but sensible-delayed. As I understand, sensible-delayed means the material has thermal mass so it releases the heat after delayed time, but I don't understand that phenomena in fenestration. I defined the fenestration with 10mm clear glass, how can it have a thermal mass which leads to sensible-delayed? Please see the image for a clear explanation. I'm very happy if anyone can help me to figure it out. Thank you.