I hope this is the right forum for this post.

I'm playing with some friends and we play multi-player all the time.

I was wondering if anyone had any experiences with rules or variants to end a game at a set time; for example, a four player game that is going along nicely, and the store closes in ten minutes.

Any variants you have tried out? For example, I thought of an "Inescapable Doom" variant, where each player lose one life the first turn, then two, then three... but that might be unbalanced.

Any ideas or suggestions?

My friends and I came up with a number of ideas inspired by planechase. We iterated these through a design cycle and tested them out. Some players didn't like the forced ending idea but when the store closes in ten minutes...

Biorhythm
(Plane)
Creatures may be played as though they had Flash. Creatures lose indestructible.
When you planeswalk to Biorhythm or at the beginning of your upkeep, destroy up to X creatures where X is your life total. Then, each player's life total becomes the number of creatures he or she controls.
When you planeswalk away from Biorhythm, exile all of your creatures and then put your General into play. Then, each player's life total becomes the number of creatures he or she controls.
Chaos: Gain control of up to X creatures where X is your life total. Then, each player's life total becomes the number of creatures he or she controls.

Venser's Foul Essence
(Plane)
Whenever you successfully cast a spell, exile target permanent.
When you planeswalk away from Venser, skip your next turn.
Chaos: You get an emblem with "Lands you control have '{T}: Counter target spell. Each player loses life equal to that spell's converted mana cost.'"

Lich
(Plane)
When you planeswalk to Lich, each player loses life equal to their life total and gets an emblem with
"You don't lose the game for having 0 or less life.
If you would gain life, draw that many cards instead.
Whenever you're dealt damage, sacrifice that many nontoken permanents. If you can't, you lose the game."
When you planeswalk away from Lich, lose half your life, rounded down.
Chaos: Lich deals 2 damage to each opponent and you gain that much life.

Traumadigm Shift
(Plane)
Exile all cards from your library. Then shuffle your graveyard into your library. When you planeswalk away from Trauma, put the top half of your library, rounded up, into your graveyard.
Chaos: Each opponent puts the top half of his or her library, rounded up, into his or her graveyard.

Worldfire
(Plane)
Exile all permanents. Exile all cards from all hands and all graveyards. Each player's life total becomes 1. When you planeswalk away from Worldfire, it deals 1 damage to you.
Chaos: Worldfire deals 1 damage to another player at random.

Braids, Disciple of Phage
(Plane)
When you planeswalk to Braids or at the beginning of your upkeep, each player sacrifices an artifact, a creature, a planeswalker, an enchantment, and a land. If you can't sacrifice at least one permanent, you lose the game.
If you would roll the planar die, roll three planar dice instead. For each blank side up, each player sacrifices an artifact, a creature, a planeswalker, an enchantment, and a land.
When you planeswalk away from Braids, you lose the game.
Chaos: Target player loses the game.

Emrakul
(Plane)
Damage can't be prevented or redirected.
Counter colored spells.
At the beginning of your upkeep, sacrifice 6 permanents and Emrakul does 15 damage to you.
If you would planeswalk away from Emrakul, instead take an extra turn after this one.

Chaos: Target player skips their next upkeep.

Divine Intervention
(Vortex: Remove the planar die.)
When you planeswalk to Divine Intervention, put an intervention counter on it for each player.
At the beginning of your upkeep, remove an intervention counter from Divine Intervention.
When the last intervention counter is removed from Divine Intervention, the game is a draw.

Infinite Evocation
(Vortex: Remove the planar die.)
Exile all lands. Additional lands can't be played. Lands have Cycling {0}.
Skip your draw step. At the end of your upkeep, draw seven cards. You may cast spells without paying their mana cost. Any creatures that enter the battlefield in this way have haste until the end of turn.