No they are programmable by time and mine have 8 cycles so any hours can be my day , same with old fashion timersThey are flexible on a 24hr light schedule.. I'm looking for a 18hr light schedule timer @Renfro
https://www.amazon.com/Century-Heavy-Digital-Programmable-Timer/dp/B00MVF16JG/ref=sr_1_8?keywords=digital+timers&qid=1554579656&s=gateway&sr=8-8Can you tag one that you would recommend USA @Herb & Suds