I'd go about 40 minutes or so - but I do NOT go back up into her room in that time - as it just winds her up more and it seems to take even longer
if I hear her yelling for her bunny (that she needs to sleep) I go in and pick it up (sometimes drops/throws it out of the crib) - that's the only time I'd go up there though - and I just give it back - say go to sleep and leave
she usually will yell for a few minutes, then lay down and go to sleep - cause she knows I'm not coming back til she does