Deadlines are toxic. Deadlines are never respected (400 % error) Deadlines are like playing poker (no way to be sure, even with KK) Estimation should be considered as what they are: a fu** estimation, not a truth. If management need it :
Else, ask the deadline. Close the discussion. If the feature is ready before the deadline, good. If it's not, what can you do ?
The rules of thumb: never sell what is not ready to be sell.