An AMC was booked on April,20,2016 (FY 2016-17) when its bill was available.
However period of AMC starts from Jan 2016 (FY 2015-16),So a provision was booked after expense was booked in 2016-17,Say on 31.03.2016 - So it is necessary to deduct tds on March when provision was created Or deduction of tds on date of booking is Ok.
Since in some case AMC will be booked on June & similar provision needs to created backwards,so when does the tds liability occurs.