I like to let the lily nail flowers set up a bit first, maybe a day or so, depending on how thick they are, then i peal the foil off before the underside is completely dry (makes it easier to get the foil off) then the air can get to the under side of the flower and it will be dry in another day. Or sooner depending on how humid it is where you live
You can put them in a cold oven with the pilot light on, or if you have an electric oven just the oven light on. The slight heat will help to dry the flowers, just make sure the oven is COLD and that no one turns it on when your flowers are in there, this usually dries ri over night.
You can also poke some holes in the bottoms of the flowers so that air can get inside and help dry them out as well.
I've dried the flat flowers and color flow pieces in the oven with just the light on before and it works wonderfully. Just remember to put a sticky note on the knob to remind everyone, including yourself, not to turn it on. 
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