uvb help plz

Hi all.

Do I HAVE TO turn on uvb for 12 hours in summer and 10 hours in winter respectively?

It seems like my little guys are falling asleep around 6 am when the sun rises, but I keep my uvb on for 12 hours from 8 am to 8 pm.

I feel like I should turn off the light at 6 pm so it will make a perfect 12-hour daylight for them.

Any advice appreciated.

Thanksnjn advance.