It can b placed till 3.30 
But u should avoid it as u will have to square it off by 3.30 if u dont square it off u will have to face heavy STT.
Also there is a funda that in last hr of Expiry day Options start trading at discount so u will have to even consider that thing (Eg. Call option with Strike 8400 with spot price at 8415 may trade between say 12-14 that is discounted premium)
Yes you can place orders until 3:30 pm.