Worried about basking area getting too hot

I have heard that if you leave the lights on for an hour and then check the temperature with a temp gun, that is the temperature the enclosure will stay at until the light is off. This gives me a a bit of reasurrance but I don't know yet how close the basking spot will be to the metal mesh at the top because my momma hasn't finished the enclosure yet. Obviously this is important for me to know because if moving the UVB light to being under the mesh(which is like 1/2 inch long squares for my enclosure, not any finer than that) makes it too hot in the basking spot, I am going to have to do something like taking the mesh lid off and attaching the lights to the wall of my room or add a reflector under the mesh or maybe do both. And of course when it is warm outside, I would be taking my bearded dragon outside to let it get some natural UVB from the sun, especially if I need to change UVB bulbs.

But yeah, I am not too worried about the bulb itself because I have done my research, I'm just worried that the basking spot might become too hot with both the heat lamp and the UVB bulb on because I don't know how close the basking spot will be to the mesh lid and I obviously want to make any adjustments to the temperature inside the enclosure before I get my bearded dragon so that it doesn't get burns.

The UVB light shouldn't wind up producing much heat so that isn't likely to be a problem. Testing temps after the basking light has been on for a while is a good idea and will give you a better reading. The temperatures should stay fairly close to that but they do tend to fluctuate based on the ambient temperature in the room. It can be tricky to keep proper temps and requires frequent checking and small tweaks when the seasons are changing in particular. Is your new tank going to have a hard top? Or is it going to be a mesh or open top? If the basking light is above the tank you can set it on an adjustable stand so you can raise/lower it to adjust temperature. If it's in a fixed top then you can attach it to a lamp dimmer or a dimming thermostat so you can fine tune the output that way. As long as the temperatures stay within a good general range (100-110 ish for the basking site) and you have a good gradient with cooler temps available elsewhere in the tank, it shouldn't be a big concern if the temps fluctuate a bit.