Acceptable estimations for software development:
- Almost certainly doable in less than a day.
- Probably doable in less than a day, almost certainly not going to take more than three days.
- Probably doable in less than a week, but who knows?
- Certainly going to take longer than a week, and nobody can say how long, but if you press me, the estimate is between two weeks and four months.
Reality prevents better accuracy.