There is a kind of misconception among many solo ad buyers that their ad should go out immediately. Most serious solo ad vendors, myself included, have already filled up their calendars for the next few days (or even weeks!).
I mail out on a first come, first serve, basis and I do not hold orders until paid for. Typically, however, I will be able to send out your ad in 2-3 days. Sometimes less.
I will always keep you updated on exactly when your ad will go out.