Your talk of providing estimates just reminds me of this scene from Star Trek TNG.

Geordi La Forge: I told the Captain I’d have this analysis done in an hour.

Scotty: How long will it really take?

Geordi La Forge: An hour!

Scotty: Oh, you didn’t tell him how long it would ‘really’ take, did ya?

Geordi La Forge: Well, of course I did.

Scotty: Oh, laddie. You’ve got a lot to learn if you want people to think of you as a miracle worker.