I usually let the decals dry for an hour or two before applying Microsol, but that's more habit than method and is not therefore the 'right' way to do it.
Some decals may not react to Microsol at all. Some may require several applications to bash them into shape. Others may over react to the Microsol and in extreme cases may even break up. I would always suggest using an unwanted decal off the sheet applied to any old bit of plastic as a guinea pig, just to be on the safe side.
Cheers
Steve