Yes, you can hide the timer for online games. Please:
Click your avatar in the top right.
Click My Account.
Scroll to Game Settings.
Toggle "OFF" the "Game timer" setting.
PLEASE NOTE: The game will still last the correct duration (1 min, 2mins, etc. depending on the game) but the timer will not be visible on the screen. This is to allow every game to come to a close and the coins are safely added to the player's account.