The respawn time for the gem to go back to the portal is exactly 30 Minutes, so don't complain about something that is actually working correctly. What I find bs is that there are still players who find it sooo funny to drown the gem with themselves to look at it respawn at the surface of the water, where no one can reach it. :\
And the best part is that NGD doesn't even care about these flaws in-game, no one knows if It's legal to drown yourself with the gem and let it respawn in an unreachable place, or if it's just a bug that is waiting to be fixed.
Oh, and what a good idea it is to invade on the day after Christmas...