CHOP states “Usually, the time for closing bids is mid- to late-afternoon.” 
 
This is not arbitrary, but a response to the practicalities faced by bidders trying to collect and assemble all the information that goes into the bid submission. From suppliers to sub-contractors to the contractors own contribution; calculating, collecting, confirming, and passing along or entering the pertinent information on the bid form all takes time.
 
Once the submission is prepared, it still has to be delivered to the location of bid receipt. Depending on the location, travel times may vary throughout the day due to rush-hour congestion, and parking may not be available nearby.
 
These factors should all be considered when the time of bid closing is determined. Two o’clock and three o’clock are common closing times. In most locations, they fit nicely between lunch hour congestion and the start of the homeward rush hour with its’ congestion, parking restrictions, and turn restrictions. They also work well if bids are coming from multiple time zones.
 
They also provide enough time after receipt of bids to open the bids the same day.
 
The recommended format for indicating the bid closing time and date has provided by CCDC Bulletin 19 as follows;

“... bids will be received before [hour:minute:second a.m./p.m.- e.g. 3:00:00 p.m.] local time as designated by the [designation of timepiece to be used] on the [date] day of [month], [year].”
 

CHOP on Bid Period and Bid Closing

To ensure that clients receive competitive prices, contractors must have adequate time to review the bid documents and to prepare a bid. The length of the bid period will vary, based on the project size and complexity. A large, complex project “out for Public Tender” may require four to six weeks for bidding, whereas a simple, small project by invited bid may only require two weeks. Market conditions can affect the bid period; for example, several projects being bid at the same time may require a longer bid period.
 
It is not recommended to receive bids in more than one location. It is increasingly common for bids to be received electronically and architects are advised to refer to Section 7.8 of CCDC 23, A Guide to Calling Bids and Awarding Construction Contracts, for information on principles which apply when receiving bids electronically. 

It is not recommended that bids close on a Friday or a Monday, nor immediately following or preceding a statutory holiday. Usually, the time for closing bids is mid- to late-afternoon. It is important to specify the time as “before” the hour, not “on” or “at” the hour. Here is an example of a well-worded instruction:

Bids must be received before 3:00 P.M. on Thursday, February 19, 2009.

The person receiving the bid should time-stamp, date-stamp, and initial the bids on receipt at the designated place of closing. Bids received after the designated bid closing time should be returned unopened to the bidder indicating that it was a late bid. No reasons for the lateness (such as accident or traffic jam) can be accepted. On the other hand, if an external cause such as a snow storm has prevented the majority of expected bidders from tendering their bids, the closing of the bid call may be postponed, in which case the bids that were received should be returned to their senders unopened.