How to enable/disable timer at will

HI I use a timer interrupt to execute the custom code that scrolls the message across lcd so I don't need to use delay. Yes the liquidcrystal does do scrolling but isn't what I want. Since I only need it to scroll if the message is over 20 chars long, how can I only enable timer1 when I it is too long but not when it's short?

Each timer has a bit in it's control registers that enables / disables the interrupt. Find that bit and set or clear it. The bit position will depend on what timer you are using. See the data sheet for the chip you are using to find out what the register name is and what bit you need to change.

amateur_25: I use a timer interrupt to execute the custom code that scrolls the message across lcd so I don't need to use delay.

Have you figured out that you can carry out actions on a scheduled basis without using delay by following the approach used in the Blink Without Delay example sketch?