I just finished brewing 30 minutes ago but in a rush to run out to dinner I forgot to take an OG reading. When is too late to crack the ale pale back open and take an OG reading? (Obviously the SG will start changing soon...).
Fermentation lag times vary so there's a chance you could get a good measure of the og when you get home. But we can't really tell you how long until your reading will be off.
I agree with gcdowd extract batches will be pretty close to the recipe as long as you end up with the correct volume. If you ended up with more or less than you were supposed to we can help you calculate the og based on your recipe and how much wort you ended up with.