How much you water seedlings depends on if they are inside (regulated temperature) or outside, and outside, if they are in pots with trays/saucers under them, or in a raised bed, and how big they are, and what the temps are. Inside I try to bottom water 3x a week, but at a pinch, if the seedlings are far enough along, they will survive on 1x a week (if I have to travel).
I know that I have managed to kill off any number of young seedlings outdoors, which were in 4" pots in a tray, by over watering AND being in hot sun. So it is better to err on the side of caution there. (Right now I am really having a hard time restraining myself from daily watering 3 flower boxes of seedlings from a cross I am particularly interested in. I also have some 4" pots in a tray that gets morning sun, but I know the dangers there, so 2-3X a week depending on the temperature.)
On the other hand, those seedlings which get planted out into the raised bed, are on drip which I run anywhere from 2-7 days a week, depending on the time of year and the temps (2, 3, or 7x). For the newly planted babies, I typically have to hand water those at least every other day, since their roots don't seem to make it to the areas underneath which are moist from the drip. (The drip is arranged as a grid, so each seedling is in its own 6" x 6" square.) I lost several babies last year, but now I know better. Once they get big enough that they can "reach down and out", I stop and they do fine on just the drip.
