Configurable list for estimate field

Add possibility to change standard values in fields like Estimate or duration

I use at best 0,5d for defining a workload (estimate) for a given activity / deliverable. Anything below this duration doesn't have any sense for a project task

This would be great if I could configure list of values for those kind of fields

I would for example configure estimate like : 4h (half day), 8h (full day), 16h, 40h (week), 140h (month)