Never thought about a timer, I have an extra one that came with my lights. I use a dome on my cloner. It's just a clear tote that fits perfect over my cloning tote. I have a 20w grow light that i put on the dome and it's on 24/7 when I'm cloning. It makes the clones grow the biggest sets of roots and the vegetation gets really thick. Within 7 day's, I'm potting clones.