Q. How long should I wait after I send a submission to a publisher before I can follow up?
A. Whether you have submitted to a periodical or to a book publisher, you always need to wait the length of time they indicate as their response time. I've seen response times vary from a few days to up to a year, so it will be important to check their guidelines or listing in the market guide to identify what that time frame is for the particular publisher. If the submission was to a magazine, then wait the indicated time, plus a couple of extra weeks for a grace period, then send an e-mail or note asking politely about the current status of your submission—giving all the details, such as title, date sent, and editor addressed to. If no response, or not a timely one, you can send them another e-mail or note indicating that you will be withdrawing the manuscript for publication and submitting it elsewhere. There is no obligation on your part to wait any longer than that. In some cases an editor never responds.
If the submission was a book proposal or manuscript, wait the indicated response time and then either send an email or letter as indicated above asking about its status, or simply contact them to let them know that if you don't hear from them during the next two weeks (or 30 days), you will be withdrawing the manuscript and submitting it elsewhere.