This is one fast doggo
and I mean really fast, like "I outrun Gods" fast.

But just how fast does can he go?

According to his entry, he has the ability to use Teleport without error, except he isn't actually teleporting but just running fast
Spell-Like Abilities: At will—air walk, improved invisibility, plane shift (DC 20), teleport without error*. Caster level 30th.
*The Chaos Hound does not use teleport without error in the conventional sense, but he becomes an insubstantial ghost and runs with near-limitless speed. While in this state he can run across or through any substance or barrier, and moves as fast as he likes, often moving between two points as if he had teleported. When in this form, he is perceived as a ghostly blur that leaves behind a lingering scent of decay and a vague dread of darkened corners and howling in the night. Spells that prevent teleportation, such as dimensional anchor, do not prevent Kezef from using this ability.
- Champions of Ruin

'Near limitless' isn't very specific, but if Kezef's ability has the same range as a 'teleport without error', which is to say from any point to any other point in the same plane of existence (= universe) then he could just instantly cross a universe using his speed.
This spell functions like teleport, except that there is no range limit...

Observable universe is 8.8e23 km in diameter
Crossing that in a second is 8.8e26m/s= 2.935 quintillion c