Rune of the Krait has a tooltip that says it should have a 30 second internal cooldown but when testing it out, waiting 30 seconds and even waiting around 40 seconds still didn’t proc the ability when I activated my elite again.
I just tested it out now and it seems to be exactly 45 seconds before you can use the Rune ability again.
Here is a video just as proof.
https://www.youtube.com/watch?v=VpzVvSBtQEQ
I can make another one showing it is exactly 45 seconds if needed.