I'm not gnosis, but I've occasionally done 1 to 3 hours in a single sitting. The "difficulty" is exactly the aversion to suffering. Well, unless you only do samadhi and enter into the bliss states. At which point, you really don't want to leave so you sit there until you fall over. (I sometimes think, meditators should participate in the 12-step program for Bliss Junkies Anonymous, except that it is exactly what vipassana is supposed to addressed).