Bottom Watering

[KBSpokane]

I'm new to this site but not to starting almost everything I grow from seeds. I've been doing that for quite a few years and I've rarely had any problem with damping off etc. I am asking for some advice on bottom watering. I have always watered from the top using a fine sprinkler watering container. I put my cell packs in an open bottomed seed flat which is placed in a closed flat. I have always watered until water started coming out the bottom of the cell packs or 4in pots, or whatever. I have let the plants sit for a few minutes; and then I pour out all the remaining water. I water again when the potting soil looks dry on top. Today I tried bottom watering, but after 3 minutes the potting soil still looked just as dry. So.......how long should I let my open flats sit in water?? Sadly, at the moment I only have onion and leek seedlings growing, but next week I'll start some brassicas and next month I can start all my tomatoes and peppers. Oh boy! Kathy