I think the standard length of time is however long you can wait without going mad! With all of the stress you've been under, I'd say it's normal. If it's more than a week late I'd take a test, although I know I personally couldn't follow that advice and would be taking a test by day 5. Actually, the last time I had a "pregnancy scare" I only waited two days, took the test, it was negative and my period turned up the next day! I'm not the most patient person in the world :-P