The consistency of the material is somewhat of a "fruit roll-up" and is to be expected, as flexibility is required for the window cling to be removed from the sheet and applied to the window. Due to heat and humidity, dry times may vary as well. If too much paint is used, it may take a little longer than overnight.
If you have difficulty removing the cling from the sheet and you see that it is stretching as you are pulling it off, work around the edges by gently pulling it up until you can pull the entire cling off of the sheet.
To prevent paint from drying out, return the cap back to the tip when not in use. If the nozzle becomes clogged use the tip of a paper clip to clean it out. Make sure to keep any left over paint for touch-ups and repair.