So Smaug is 5-6 months old, and she has been going to sleep earlier than normal when it has been a bit colder. Do younger bearded dragons that don't go into brumation go to sleep a bit earlier than normal because it is cold?
Are you saying temps inside the enclosure are colder? Ambient/room temps shouldn't affect them, though changes in the amount (hours) of light they receive may. I've recently gone from 12 hrs of light to 13 as the days get longer here. He's adjusting, but more slowly than I thought. He starts to look for a place to sleep when the UVB turns off an hour before the basking lamp.
Do you take him out often? Running around in cooler room temps may affect stamina/tiredness.