the heated seats have 3 modes, high low and boost. when it is cold enough, the first few minutes of high will be boosted to gain temperature quicker followed by a drop to high for 10-15 minutes, concluding with about 45 minutes of low before shutting off completely.
there is a temperature sensor in each seat, as such there is also the capacity of the ECU to cut out the heat sooner than the full ~60 minutes.
there have been a handful of replacements of both the seat heating element due to resistance being off a bit, which will make the heating not fit the ECUs algorithms. one vehicle had heat for 4 minutes on high and 10 minutes on low, replaced element, but it still only operated for less than 30 minutes total. this was with no one in the seat, so as such it'll act differently with a body in the seat.