There are estimates and there are commitments.

Estimations attempt to gather and communicate risk while Commitments are guarantees.

Commitments are rare and virtually non-existent. In general a functioning Engineering org does not provide Commitments until they're so far along on a project as to make the Commitment virtually useless to the rest of the organization.

Estimation Types

All estimates, be they 30/60/90's or T-Shirts are always given in individual engineer time. Not team time. If something cannot be fit into one of these two structures then it needs to be further broken down for estimation to be of any value to the business.