Here are two methods to hide last seen from whatsapp...!!!

>>Manual Method
>>Application Method

>>>>Manual Method

To disable this last feature of whatsapp , First of all we have to understand how this
feature. Okay Let me tell. Whenever you open whatsapp it updates your last online time to
its database using your internet connection. So if you will disable your internet connection
before opening whatsapp then it can not update your last seen time to its database. So
simple manual solution is that disable your internet connection before opening
whatsapp.

>>>>Application Method

There are many application available on Google Play Store to do that which you did
manually. But I am going to share one of them because I tested it first and it is working
fine. So here are steps , just read and follow them carefully.
By :-blacklisthackers

STEP 1:
First of all INSTALL WhatsApp No Last Seen(SEE LINK IN COMMENT) from playstore.

STEP 2:
Now just configure this app using tutorial given in the app.

STEP 3:
Now you have to do nothing , now its app headache to hide your last seen from your friends.

WORKING

Let me tell you working of this app. This app will recieve your whatsapp and will give you
ability to reply the message. When you open whatsapp to reply, it will automatically
disconnect from internet and when you will come back to home screen it will automatically
connect you to the internet.

Enjoy & Visit again for new updates.