If we "bought" a pc for home business Black Fri 2016 using 18 mo. no interest and paid it off in Jan 2017 do we claim it on 2016 or 2017 return?

[Opus 17]

Assuming the computer meets the other tests to be depreciated or expensed (must be used at least 50% for work, etc), the date you purchased it is the date you acquired it from the vendor and placed it into service.  Paying the vendor with a loan that you are obligated to pay back is what starts the clock, not whenever you happen to pay off the loan.