I'm sometimes a cheetah in the free
Sometimes a sloth in a tree
I'm time itself ofcourse
The fourth hour
I'm in a bit of rebellion, I changed dimension
Measure me all you'd like
I'd only taunt your instruments
Unless you get it right of course
A dipleidoscope, pff fancy, but no
Not useful any longer
A king might be able to help you
I flew over here. Now you surely got my number!
Where am I now?
I entered the savannah at noon
If that helps
Answer is ~one word
Edit: Made it a little bit easier
The savannah line un-far-fetch'ified => 'I was a cheetah at noon' (this hint is only useful once you've figured out what time changed about his nature).
Hint 3: (not useful in simplified version)
The fourth line relates directly to Hint 1. To make the fourth line correct: Change 'dimension' for 'hour'
He will taunt you if you try to measure time with a watch. A instrument which may work is a ruler or even easier a text editor which shows line numbers
There are some lines without a lot of significance such as the sloth line, the unless you get it right line or the last line.