How often to feed with AB system

I've no experience with the AB nutrients, so take this advice with a grain of salt.

If your garden does not have a timer, then you should probably monitor feeding manually!

A simple solution is to take some blue painter's tape and a Sharpie, and write the date you added nutrients on a bit of tape, stick it on the garden somewhere. Or set up a reminder on your preferred calendar app. Or both if you are forgetful like me, LOL!

Sprouts usually don't need much water the first couple of weeks, so you are likely fine at the moment. 

After two weeks, a water change is a good idea, and it won't hurt the plants, even if the water seems fine and the plants have only just begun to barely drink. Up to you though. Some folks just add nutrition and only change out the water monthly. For what it's worth, changing water out is easy if you have a siphon!

My own tap water is a bit tricky, so I prefer the every two week schedule so pH doesn't get out of line.

ftlaudmom, if you change the water in a garden before 6 weeks, the seedlings may fall over flat and need propping up for a few hours afterwards. This happened to me again just last week with a tomato seedling, although I replaced the water immediately after siphoning the old water out.

Some seedlings are very sensitive to having their roots exposed, or to any change in water temperature. My seedlings always recover, as long as I prop them up with a little trellis made of coated plant-tie wire, or with a grow dome.

The AG blog used to have a post showing how to make individual wire trellises. I don't know whether it's still up.

pfunnyjoy, Yesss! Your props look almost identical to the ones that I remember from the AG blog. (Better, actually.) These work beautifully whenever a spindly seedling needs a bit of help standing up.