As mentioned in many suggestions about weather options, the transition between wet and dry, or dry and wet should be smoother.
With heavy rain its ok when the road is soaking wet in less than a minute.
But with light rain it should last a bit longer.
Transition from wet to dry should last longer than 2 minutes.
I tested it after update 12 with a 45 minutes race, and 4x time multiplicator.
But time multiplicator and race length do not affect the transition.