Garuda/Carby have some windup using contagion but it shouldn't matter at all. The only way it would be a problem is if you were using it when a dot had like 4 seconds left and dropped off first, instead you should be using it just after you've applied them all, or if it comes off CD with them all having 10+ seconds left.

You should also watch RS's timer since you want it and contagion available at the same time