A word var can count up to 65,535. If your Timer1 interrupts happen every 20mS, then count up to 3000.

It won't be right on the money for 1 second with your delays, HPWM, etc, in your Timer1 interrupt handler, but you can adjust for overhead if you need it closer to 1 second exactly.

You could also use a Timer0 interrupt to increment your counter.