The longer you leave it to sit, the thicker it becomes. I always have to leave mine for 5-10 minutes before doing it, otherwise it's all runny and waterey...and forget trying to comb THAT into your hair !!!
Also, it helps (I know the pictures say to comb it onto your hair, but it helps to pic out the strands or chunks you want to do lift them up and comb through or onto them that way, then lay them back down.
My hair is extremely long, so the roots to half way down the head are always highlighted nicely.... but the bottom half doesnt even exist!
picking up the strands helps when you need a second application to reach all the hair down to the end of the strands, and makes for a more even coating.
Hope this helps
have fun & happy chunking!