If you purchased goods on 31st July also you have received the material and bills on 31st you pay Tax on 31st...
Your employee ll be receive any supplies on travelling for the period of 10th July to 15th July. He ll reach in office on 17th July and give the details on 17th. Some bills received from URD on 13th. But, He give the details on 17th and you account it on 17th. Then you ll be pay Tax on 17th July....
If you don't pay on 17th then you calculate interest 18% after the payment date....