How much you need to mist will depend some on your cage type and your ambient humidity levels
As far as setting your mister up, I would get a digital timer for it rather than using the timer on the unit. You can set your mister duration, turn the unit on, and then connect to a digital timer set to go off for one minute at each of your planned misting times (only need a minute since it won’t run any longer than that) If you want it to mist for longer than one minute, you’ll probably need to set multiple one minute intervals. My guess the main issue you’ll have is keeping the reservoir full, it’s not very big