that's more or less up to you, how your set up is built and how much water your set up can handle.
But... there are some basic guidelines:
You want things to dry out over night, so make your first mist shortly after the lights come on (give him time to warm up before spraying him with possibly cold water)
I also have my last mist come on a hour before lights out to help things dry out good.
My set up can handle a decent amount of water and I have NO DRAINAGE system. Most of my mist gets funneled into by baby tears plant or evaporated off the leaves. I have my mists set for 1 min long and up to 1min 45sec at a time. I also a dripper which drips about 4-5 drops per minute (1 drop per 10-15 sec) and that's plenty to keep standing water on my golden pothos.
I also have a humidifier plumbed to put humidity inside the enclosure, its on a few hours before lights up and off a few hours prior to lights off.
I tend to have most moisture in the morning (after I leave= no opening closing door disturbing humidity) and let things become less humid in the evening when im around. So I would mist at 7am, 8am, 9am, then switch to 11am, 1pm, 3pm, 5pm, 7pm. for 8 cycles.
I find this to make the most sense in programming intervals. But for how long is up to you.