The permanent +10h Idle income time purchase, "increases your idle income time for dungeon revenue", which only affects the crystals generated/converted in your dungeons.

Your dungeons will produce idle income for 2 hours (as a base value). This value can be extended by getting this permanent boost. It will increase the idle income time of your dungeons (crystals) from 2 hours to 12 hours! It does not affect the Idle XP in the village siege (which is located in the village, not in the dungeons).