Most of the work happens in the last hours. General contractors receive sub and supplier prices late, compare them and close their number before the deadline.
Example: an equipment supplier sends its proposal the afternoon before. On bid day morning a late addendum changes a quantity. The supplier sends a revised price with the addendum noted.
Send your proposal early enough for the general contractor to read it. Put the price, inclusions, exclusions and addenda on the first page. Stay by the phone. Estimators call with scope questions right up to the deadline.