Is it possible to short sell on crude oil for a week or more?

I want to Sell first in normal and hold the position for 10/15 days then Buy back later on Crude oil. Is it possible?

Absolutely, you can short it and hold it till the day of expiry.

Expiry of crude is on the 19th/20th of the expiry month. So you can hold it till end of that day. Check this.