Uncle Time is Father Time's brother, the deity in charge of Timeless Space. He is also the pet store owner who sold Bun-bun to Torg [1]. It was he who returned Bun-bun to his original timeline after both of Bun-bun's trips into Timeless Space, Bun-bun having "solved the riddle of Uncle Time". (Actually, Bun-bun had never even heard of the riddle, and it is in fact never stated, though the answer appears to be diving into the Oceans Unmoving.)
In ancient Mohkadun, Uncle Time was known as Tempest, god of Fate.