Hi,
I didn't use msp430 but here is a general idea, I tihnk you can easily adapt it to this controller
You can write a timer interrupt that outputs 1 from an output of MCU1 after counting for a while and resarts at the beginning of the main function. That output should be an interrupt to the MCU2 which will enable timer of MCU2. I think you can also deal with a few cycles lag by adding some null commands before restarting MCU1 timer.
regards,
Erhan