Follow this game manipulation:

When the tiles are displayed, click the Menu button. Move the menu out
of the way. Study the game screen. Determine your next move. The clock
does not advance during this time. After you determine your next move,
click the Resume button on the Menu. Make your move. 

Click the Menu button at the top right of the screen. This again stops 
the clock. Move the Menu panel to the side. Determine your next move. 
Click the Resume button to start the clock. Make your move, click the 
menu button yo stop the clock. and so on. This can be performed on any
level. It's especially useful at Level 78.