by entering the date it was placed in service (or disposed of), the software knows not to depreciate for the whole year.

Under normal circumstances, that would be true, however this is a short year for the business (only 5 months).  The depreciation for the short tax year should be 5/12 of the total allowed.  The date purchased and placed in service are identical.  I need it to only take depreciation for the months he owned the business, not for the half-year as normal.

I've never heard of a short year Schedule C, are we sure that's a thing?  The (1040) tax return covers the entire calendar year so it's not a short year return.

I've seen short year Schedule Cs.

What if the business started in August?

Or was incorporated in May?

If the software won't do it you will need to override the calculation.

That's true, however, the depreciation rules state you can only take depreciation for the part of the year you own the business.  I realize the rules were written mostly for entities other than Schedule C (this is a single member LLC).  I have gone back and forth in my mind about how this should be reported.  

That's kind of how I feel!  I hate to override it this year because it will need to be overridden every year till the life is up.  

Not if you compute using MACRS formula instead of Tables . Does ProSeries have that option?