In Project, the default task duration unit is days, but you can change it to be minutes, hours, weeks, or months:
Choose File > Options.
(In Project 2007, choose Tools > Options.)
In the Project Options dialog box, choose Schedule.
Under Scheduling options for this project, in the Duration is entered in list, select a duration unit.
To use the same setting automatically in all future projects, select All New Projects in the Scheduling options for this project list.
Tip: Need to change the work duration unit? Use the same process, but change the Work is entered in list instead.