With both my LO's I got really excited when I dropped but for me it was not an immediate indicator of going into labor. I think the general answer it could a couple weeks (depending on how far along you are of course!) to days.
If I remember correctly I dropped about a week prior to giving birth
I'm not sure when I dropped or if I ever did... But I never went in to labor had to get induced 9 days past due date... It was all good though... I'm curious about this question from others too....
I went into labor the same night I dropped with my first. (Bowling ball in my pelvis sensation). Due date is tomorrow with this one and still haven't dropped - although everyone who sees me feels a need to tell menI have...
Re: When a baby drops
If I remember correctly I dropped about a week prior to giving birth