Welcome to 420..qcclosetgrow.
It all depend's on what type of medium your using.
Some soil has added nutrient's and will not need feeding for week's.
also here's a link to uploading photo's.It's a bit easier then using a link.
I have never used any MG soil but have followed a few that have.I do know they have added nutrient's mostly slow released and last for months.I don't think the seed starter mix has as much fertilizer as there regular soil,so it may be good for starting plant's.Idk much about using MG but here's a link to a good read journal dealing with MG.It's long,but the start of it is were she is using MG. 420 Magazine ®