I had trouble with this timer at first too.
'day start' is how long you want the mister to mist. 'day stop' is how long you want it to be off in between mistings. The same goes for 'night start' and 'night stop'
The last function you have to set is when the 'daytime' period starts and when the 'night time' period starts.
I'll give you an example. Say you set the 'day start' to 3 minutes and the 'day stop' to 3 hours, with the daytime period beginning at 7am. The mister will mist for 3 minutes, every 3 hours, beginning at 7am and going until the night time period that you set.
I hope this helps a little! It's a bit more difficult to understand than the ST24 timer.