It depends on your loc extension method. Some methods of loc extension (such as those attached by braiding) can be done right away, and others, such as crochet hooking (which is uncommon, but I know of a few loc’d Tumblr users who have successfully done so) must be done after a waiting period. All locs can be extended, though, so if it’s something you want, you’ll eventually get it!
If you are getting the extensions done at a salon, as your stylist what your options are. If you are doing them at home, video tutorials on YouTube usually mention whether there’s a waiting period involved. If you find a method but are unsure of the details, send us a link and let us know what your questions are! We’d be very glad to help. 🙂