When you open a quotation request you will see two timers in the right top corner of the page, similar to this picture:
The expiration time shows how much time you have left to submit your quotation. Please bear in mind that you can no longer submit your quotation after the timer has expired!
In the example the shipper has 21 hours and 18 minutes to make the actual booking after the expiration time has expired.
But they can decide to book the shipment at any time during the request phase.