At 20MHz, if you're using the internal clock, Timer1 will count to 65,535, then roll-over on
the next tick in just 13.1072mS with a 1:1 prescaler.

If you set the prescaler to 1:8 it would take 8 times this period before it rolls-over. The
only way you could use Timer1 for a 10 second delay period would be to monitor & count
over-flows until your 10 second period is up.

Unless you're just trying to learn to use timers, a long pause would be the easiest.

Steve has a nice utility here: http://www.mister-e.org/pages/utilitiespag.html you might
find helpful. Check out the timer helper.