The relevant solicitation provisions are found in FAR 52.212-1, Instructions to Officers:
Offerors are responsible for submitting offers so as to reach the Government office designated in the solicitation by the time specified in the solicitation. If no time is specified in the solicitation, the time for receipt is 4:30 p.m. local time on the date that the offerors are due.Further:
Any offer received at the Government office designated in the solicitation after the exact time specified for receipt of offers is late and will not be considered unless all of the following exist:An exception to the foregoing are cases where there is acceptable evidence to establish that it was received at the Government installation designated for receipt of offerors and was under the Government's control prior to the time set for receipt of offers (difficult for a contractor to prove), or if the solicitation is a request for proposals and only one proposal was received.
- it is received before the award is made,
- the contracting officer determines that accepting the late offer would not unduly delay the acquisition and
- if it was transmitted through an electronic commerce method authorized by the solicitation, it was received at the initial point of entry to the Government infrastructure not later than 5:00 p.m one working day prior to the date specified for receipt of offerors.
A recent decision illustrates one of the pitfalls when a bidder assumes too much. Washington Coach Corporation sent in a proposal via email where the return portion of the email transmittal showed that the Government received the proposal before proposals were due. Evidently the Government's email had a size restriction for attachments (which was not mentioned in the solicitation) and it got stuck in the Government's email system. The CG noted that "... it is an offeror's responsibility to ensure that an electronically submitted proposal is received by - not just submitted to - the appropriate agency email address prior to the time set for closing."
While this rule may seem harsh, it alleviates confusion, ensures equal treatment of all offerors, and prevents one offeror from obtaining a competitive advantage that may accrue where an offeror is permitted to submit a proposal later than the deadline set for all competitors.
See Washington Coach Corporation, B-413809: Dec 28, 2016.