I will always respond to PMs that the ladies send to me, so long as they are nice and not critical of my posts, that is.
WRT to how long to wait, I will sometimes add that I have sent PMs to several ladies and I hope you get back to me before my limited times are full. True story, and sadly I have had to tell a couple of very hot ladies, that I have already made plans for that week, and we look to see what might be possible the next week. Not enough hobby time or dollars to satiate my desire for ATX hotties.