Customizing time and currency units with the Project Formatting inspector
Units selected here are used to display durations and effort amounts. You can plan in hours, days, or whatever works best for you. Note that, in duration fields, if you enter a number without any units, OmniPlan assumes that you mean the smallest unit that is enabled here. The Dates Display settings below control how much detail is displayed in dates such as task start and end dates and milestone dates. If you want to go further than just customizing the display of durations, you can force OmniPlan to schedule in whole hours or whole days with the scheduling granularity setting in the Project Information inspector. 
Your work day may be any number of hours. These conversion factors determine how to add up hours into the larger units. 
The effort conversion factors don't actually change the working hours for the project, just the way durations are entered and displayed. To change the working hours, visit the work week section of the Calendar view. 
Use the Dates section to choose whether to include seconds, the time of day, or both in your displayed dates.
Choose a standard currency format from the list, or just type the number 1234.56 in the format of your choice. Duration and effort values have the following abbreviations. Which units are displayed, and how hours add up into bigger units, is determined by the Formatting inspector above.
s — second
m — minute
h — hour
d — day
w — week
mo — month
y — year
Note that the date headers in the Gantt chart and resource timelines can also be customized, with the Display preferences.