Nothing written in Clay, I always estimate on 50 mph with another 30 minutes. it all depends on the roads, I am quite happy to do a 6 hour tow including in that a 30 minute break, for fuel and a pee. But, if it is a twisty or rising and climbing tow, that drains you mentally. So 4 hours.
In the UK with no time or ferry time restraints, just go with the flow.