BP active during the day

[Caali]

It's 10PM right now and I just checked the humidity is at 71%... I've just put the fan on but I feel as if it'll cool down the tub as well so the heat will go down too in the cold side, does this matter much?

If you use a heat mat, it should be ok. The temperature can drop one or two degrees at night.
The warm side should stay the same if you have a thermostat attached to the heat mat. The could side might become a bit cooler but unless it goes under 77 degrees at night and 78 degrees during the day, it should be fine.