When I led a team of estimators I asked my team to take a recess every time I saw that they need one. The day ended after reviewing where we were till then . The next day we started talking about last night's game. Then we returned to the number crunching exercise . When the entire estimate was complete in draft we invited the design team to have a look .
This could be the last day so we finalized the estimate , the basis of the estimate and necessary backups .
When I was told that the fedex guy has been scheduled, then I made an announcement that the estimate should be placed on my desk and I went home .
The last morning with a fresh cup of coffee and a fresh brain I'd review the estimate alone for a few hours.
Invariably there was a mistake and we'd look at it together.
The estimate was good to go.