In addition to what the others said: you can get a power strip with a built in timer. A lot of timers only have one outlet on them, and if you have a fluorescent UV light you'll need two outlets.

https://www.amazon.com/Zoo-Med-AquaSun-Aquarium-Controller/dp/B003NWMQO0

^ This has a timed side for your lights (and anything else you might only want on during the day, like a bubbler?) and an always-on side for the filter and heater.

Turtles should get some dark time at night for sleeping, I wouldn't leave the lights on for days at a time (especially if there's a risk of the bulbs overheating)