Well, things will no doubt be a bit to the bullet-proof side, but knowing what film you used might help create a more precise guess. Negative films have pretty good tolerance for over exposure. But also, some films have considerable reciprocity loss at long exposures; that is, if the reading called for 5 seconds, you might actually need 8 or 10 anyway. If both situations apply to your case, you might get something usable. If it was slide film, things will probably be pretty washed out.

That's my current 2

Ah, and welcome to APUG!

DaveT