About Media Deadlines
If you want to advertise your products in magazines and other periodicals, remember that issues are usually prepared well in advance. So you need to find out the publications’ “lead time.”
The lead time is how far in advance you must place your ad in order to have it run in a particular issue. For example, if the magazine has a three-month lead time and you want your ad to run in December, you must have the ad ready to go by October.
(Source: The Complete Idiot’s Guide to Direct Marketing)

Comments