Some parallel worlds have different time-flows, like the fabled dwelling-places of the elves: those who visit them under the hill for a night return to find that years have passed in this world. Perhaps it is the gate leading between the worlds which causes the alteration. If a gate were 'misaligned', the shift from '| |' to '| \' or '| /' as it were would lead to that difference, much as a light-beam split and bent by a prism ends up taking a longer path. There might even be a mathematical function linking degree of misalignment to alteration of time-rate.
A long time ago. Final fantasy III came out with a new approach to learing magic. The characters would be equipped with espers(magical beings) and as they fought more battles, they would learn spells from the espers. What if a similar approach to learning magic was applied to a P&P rpg?