The standard CS351 S'05 policy on late handins, as documented in the class syllabus, applies to the final rollout.
For Milestone 1, the official due date is Mar 11, 11:59:59 PM Mountain time (immediately before the start of Spring Break). Any handin between that time and 11:59:59 PM Mountain time on Sun, Mar 20 is considered to be one day late and incurs only a single 15% late day penalty (or a single slack day). Thereafter, the normal accounting process resumes, incurring 15% per 24 hour period, or fraction thereof. E.g., an M1 submission on at 4:32 PM on Mar 15 would be one day late, while a submission at 12:15 AM on Mar 21 would be two days late and a submission at 9:42 PM on Mar 22 would be two days late.