Had a look around and was suprised to see that Warn doesn't list a duty cycle, they only say it's 'intermittent'.
But I did find an analysis on line of a 9.5XP.
Winch comparison - Understanding winch ratings - mikesjeep.com
He theorizes a 77% duty cycle, meaning it can winch for 11 and 1/2 minutes out of a 15 minute period.
The actual duty cycle is unknown and he did not test 30 units to failure to discover a duty cycle.
We might assume that other products are designed with a similar spec.
However there may be a different spec between a full size vehicle and SxS winch.
So, my take on all this, pay attention to how hot the motor casing is if running the winch for more than 5 minutes continuous.
(The motor over heating as a failure point is an easy to evaluate parameter, there is also the possibility the motor power controller will melt first but its difficult to evaluate when balls deep in mud)
Interesting side note, the Badlands winch (from harbor freight) is theorized at a 5% duty cycle, 45seconds pulling at max load with 14 minutes 15 seconds cool down. Not my idea of a good value.