The skills "repair" and "cold Slower" have fully variable cast time and no Fixed cast time.
So I should be able to insta cast them with the formula : Dex X 2 + Int =530 !!
But I am not able to insta cast them with >530 total according to the above formula.
Here my stats are
Dex - 130+52 - 182
Int - 130+53 - 183
Total according to formula = (182X2)+ 183 = 547