Yeah the cheap mechanical timers are fine. I use the grounded ones that have dual outlets so I can control multiple lights with the same switch if I want to.
Do you have a 24 hour or 7 day timer?
The 24 hour timer will work on same settings everyday of the week automatically?
For example if you want the lights to turn on 8 am and off 8 pm everyday, a 24 hour timer will automatically do this 7 days/week?