I'm looking for a semi-automatic timer.

I grow trees in Alberta in containers. I can't just use a repeating cycle, because the trees needs vary too much depending on temperature, cloudiness, wind, size, and season. Lot of poke finger, lift tree out of pot to determine when and how much to water.

I currently have a box full of those $10 mechanical timers. This way I don't have to be there to turn off the water. What I want is a simple timer with a delay. So that I can set the first dial for 5 hours, and the second one for 1 hour, and then 5 hours from now it will run water for 1 hour.

I want it simple to set. 10 seconds max. All the electronic ones seem to think I want to do this every day. Not just once.

Anyone got ideas?