Are there different endings for Antichamber?

Nope, there is only one ending.

The timer is explicitly there to demonstrate how pointless it is. Much of the game is about breaking gaming conventions.

There is only one intended ending.

However, if you like seeing another, likely unintended ending, try to perform the last action in the game while jumping backwards out of the sphere. If you succeed, you then can watch the ending unfold from the outside, and keep roaming around the final map until the screen fades and the credits come on.