The transaction is terminated at the end of the third business day before the 25th calendar day of the month before the delivery month. If the 25th calendar day of the current month is a non-business day, the transaction shall be stopped on the third business day of the business day before the 25th calendar day.

If 25th of the current month is a working day, the last trading day of WTI contract in the first month of the current month is the third trading day before 25th.

If 25th of the current month is a non-working day, the last trading day of WTI contract in the first month of the current month is the third trading day before 25th.

Usually around the 20th.

You can go to NYMEX's website to see the specific rules of all transactions!