I found that it can take several hours for the viv to warm up to the temp you set using the dimmer stat. noiticed this several times while working out best placement for lamp and thermometers. my stat is a habistat with a max temp on dial of 92F.
have also noticed that temp will take longer to build if humidity is low. What are your room temps at? if your room is cooler as well it well take a bit longer to reach desired temps.
the things you can do when you have an empty viv. mine is about 2'L 1'D and bout 20 inches high. lamp bottom is about 15inches from floor. heat lamp guard bottom about 11inches from floor.and it takes 1hr18min to drop from 88f to 72f when the power goes off.
you could try moving your probe slightly further away from direct light source .
sorry if this is no help.
0.4.0 Royal Python 1.0.0 Pastel Royal 0.1.0 Spider Royal 1.1.0 Carolina Corn Snake 1.0.0 Normal Stripe Corn 1.0.0 Yellow Bellied Turtle
it seems to be one of those things that is not essential to do. like having a basking area where temps can be 90f-95f. several site and info blogs i have read mention that royals can easily tolerate a fall of 75-78f and night time.
If only I had my royal now i wouldn't feel like such a fake as I have no experience to back anything up with.. can only pass on what I've read.
0.4.0 Royal Python 1.0.0 Pastel Royal 0.1.0 Spider Royal 1.1.0 Carolina Corn Snake 1.0.0 Normal Stripe Corn 1.0.0 Yellow Bellied Turtle