When you setup up portal, you can set up a timer. Two different types of Timers, first one would be a basic timer, were the player would have to stand in the portal for x seconds and the second type would be a continues timer always going. And the second one would be a server wide timer.

I'm all for this idea! Currently, the closest thing we have right now is to disable teleportonmove, which makes the portals act like nether portals instead of end portals. It also does it globally, so it's not too useful.

I love the idea of timed portals.

"The train will depart in 10 seconds." <- something like that when you walk into would be nice.