some issues with great stuff

[arielgasca420]

I used some of my great stuff last night on plexiglass (because I could not find polystyrene)
I sprayed it on, left it in my garage over night and today it looks like it expanded 25%
I tried it again today and this time I left it outside. Hopefully it expands a little better out in the elements.
How long does it effectively expand for?
I know it can expand slowly for up to a week, but I expected it to expand 50% within the first 8 hours.