They do have what is known as "rolling rest". If you fly a 6 hour day and go to the hotel you are still technically on duty for another 8 hours (14). However if they have not called you at the end of the 14, you are still considered to have been in rest for those 8 hours in the hotel, hence they could call you out 2 hours later as you have had your 10 hours of rest. The only way around that would be to leave you at the airport for the 8 hours and then put you into a defined rest period....pick your poison
. In my experience that very rarely happened most of the trips were scheduled for the next day, but there is always the possible recovery flight or pop up.