You always submit the response to a bid one day earlier than the customer requested. You do that to demonstrate that you are in control. Of course, you can still submit your bid on that day. If you have to choose quality and need extra time, take it.
Suppose you finish much earlier. Then don’t submit it yet. Indeed, it may give the customer the impression that you have spent little time on it. Even if you don’t have to spend that time because the customer’s question is so spot on for you and you already had all the answers ready, you don’t want to give him that impression.
When then? If the customer asks for standard and requires speed and you are sure to have a top-notch response.
If you can’t make it, sometimes you can ask for extra time. With tenders, this rarely works out just before the deadline. With RFPs, sometimes you can. Then be sure to explain why you want it. And then not be because Pete was on vacation. A customer is often sensitive to reasons such as “we’ve inserted an even better solution, and it requires a little more explanation” or “we want to do one more quality check to ensure we’re answering all your questions correctly.”
The method of submission is almost always indicated in the application document. Some companies want to receive it in the mail; others have a tool for that purpose. Always test this tool before submitting anything. Nothing is more annoying than struggling with a tool five to twelve. And do you send something by mail? If so, always ask for an acknowledgment of receipt. It is an excellent contact moment when customers have not specified how they want to receive it. If you have a phone number, please call. Do so at least a few days before the deadline. That shows you are nicely on track.