Helpfully arranged by class.
Warrior: Endure pain + Increased stance duration + Axe/Mace, Axe/Shield, or Greatsword. Fear me as a bonus.
6.25 seconds of damage immunity. 2s stun, potentially AoE. Tons of burst damage. Timewarp has a 10 second duration. You’re playing a tanky class. Bonus points if you took the trait that makes it auto activate at 25% health. You can, and should walk right in there, and start bursting people while they can’t do a thing about it. Afterall, if they leave the small area that timewarp is affecting, they lose the bonus. Add your two dodge rolls to this, and you can be immune to damage for the ENTIRE duration. With a cooldown more than twice as short.
Guardian: Save Yourselves + Shield offhand + anti projectile defenses.
They hit you, they take damage. You take less damage, you already regen. You use projectile shield to force them out of the timewarp if they want to attack you. Not really ideal, but retaliation is good in general.
Ranger: Um… yeah, running away probably. Ranger isn’t that strong of a class, or one I know that well.
Engineer: Knockback turrets + ranged deployment turrets + More knockbacks. Also grenades with range bonus.
They can’t attack you if they’re CC’d. They can’t attack as fast if they’re out of timewarp. Also, 1500 range lets you sit 300 units beyond the range of everyone in timewarp.
Thief: Stealth. Dagger/Dagger dual skill.
Spam invuns, stay out of sight. You can pretty much pop shadow refuge just outside of timewarp, and be safe unless there’s something like an engineer that can literally spam ground targeted skills. Or you can just creep around them with stealth and wait for it to wear off.
Elementalist: Bunker build.
You’re already obscenely tanky. Sure, they might get -you-, but if they, even in timewarp, have to throw all their cooldowns at you then auto you, odds are your four allies are going to kill them anyway.
Necromancer: Fear. Lots and lots of fear.
They walk out of timewarp, they lose quickness time. Also, group CC, they can’t move if you spam it.
Mesmer. Blurred frenzy/ distortion if possible.
Everyone. Back off, wait the ten seconds out.
It’s ground targted, it isn’t chasing you, it has a long cooldown, and the area isn’t too big. Two dodge rolls will probably get you a decent amount of the way. Battlestandard + Endure pain is 100% chance of rezzing entire groups. Guardians and elementalists can take entire groups and live for obscene lengths of time. Thieves can disengage from combat at a whim. You can’t counter any of these by simply moving out of range. It’s strong, sure, but it’s certainly not gamebreaking.
Oh, and fun little fact, cooldowns don’t cool off any faster in it. Chilled still works wonders.