I was looking at the code for validating dates for the new assignment.
Considering the ranges tested, I was wondering if the first and last tests should allow the submissionfrom and compared dates (duedate and cutoffdate) to be equal. I suggest that these two comparisons should use >= to prevent the case where the dates are equal to allow students to have time to submit. The validation strings support this assumption. I can't think of a contradictory case (perhaps an offline assignment).
(Damyon: Sounds correct to me - but the upgrade code will need to do something sensible for assignments with these dates already set to == - and if this is valid for offline assignments that will need special handling)