I don't remember what project I was doing but with 2 timers that shut off themselves and start another that isn't the case.
Timer1 starts, sends message, starts timer 2, stops.
Timer2 starts, sends message, starts timer 1, stops.
Timer1 starts, sends message, starts timer 2, stops.
.....etc
This goes on like this. Stopping the timer then restarting removes a pause from the delay.
Test it out if you like.