Thanks redmarine.
Now I see that I still have the same problem, my skill should deal 100 damage per second channeled. So:
hero1 start channeling
after 0,9s
hero2 start channeling
after 0,1s
hero1 and hero2 got 100 damage.
How can I avoid this?
(Well, if only say "use jass" It will be bad, because I can't really see how to do that with Jass)