With online Whatsapp you can do it, download this free app and you can see if they are online or what time is last connected without update your time connection. All in a completely anonymous way and without entering the whatsapp.
Launch the app the first time and it will ask to use connection ( Wifi - Mobile Data - Wifi + mobile data ). After it will load the whatsapp contacts list, select the one you want to see and whatsapp window opens. Wait until the connection time appears and press the close button.
Note: Some iPhone users have selected the option to not show online status so you can not see these status.
Unofficial Product. This application is not endorsed by or affiliated with WhatsApp Inc. WhatsApp Messenger, its name, trademark, and other aspects of the app are trademarked and owned by their respective owners