Sounds sensible to me. For longer tasks, I also think it's useful to say (where practical) "I'm really not sure because there are too many unknowns but if you l

Sounds sensible to me. For longer tasks, I also think it's useful to say (where practical) "I'm really not sure because there are too many unknowns but if you let me work on it for X hours first I can provide a more accurate estimate then". I think the important points are to always caveat estimates, build risks + unknowns into the estimates, update estimates as the situation evolves and never allow yourself to commit to an estimate with too many unknowns.