Alright, there's just one thing here that should be stated:

Night drop is NOT needed unless you're breeding!!! In fact, it's not really wanted.

The goal is to keep the warm side 90-93 and the cool side 80-83 with an ambient of at least 80. All the time.
I finally got my new tub up and running well, with her in it now, and found the way to keep those temps up at night (when my room temp drops to around 69). I have one UTH on each side of the tub, one on t-stat the other on a rheostat on a timer. The tub is insulated with cork on the back and sides, and I have a day and night lamp about a foot or so above the tub top with 50 watt day and moonlight bulbs. The bulbs boost the ambient to around 80 while the UTH's work the gradient.

Whereas a little drop in temp at night is acceptable, and expected in some places, you don't really want the ambient to go below 77, and certainly never below 75.