This particular example doesn't reload TMR1L & TMR1H. It just lets timer1 count up to its max 16-bit value, then overflow.

A simple way to extend the time would be to increment a variable counter in the interrupt, then toggled the LED after X number of counts, and reset the count back to 0.

Or, on the 18F67J60, you could use timer0 in 16-bit mode with a prescaler of 1:256. That would give you >3 seconds until overflow.