Freeze it right away if you aren't going to use it right away. There are a million things you can do with homemade stock. Stock is gold, baby, GOLD!
Yep. Next time you want to make sauce or gravy or stew or risotto or whatever, you'll be glad you have it on hand.
Freeze it in small portions--pints or cups, certainly nothing bigger than a quart. That way you can thaw and freeze on an as-needed basis.