When am I required to log? Under 26k & over 10k

The clock for the 8 hour break starts as soon as you go on duty, you have until the 8th hour from when you go on duty to take a 30 minute break, no driving after the 8th hour until this break is done. In your example you could take it at the 3rd hour then you would have 8 hours from that point to drive before needing another half hour break, you do not have to wait until after you have actual driving hours accumulated.