I didn't date the cans, but off hand they were more than a year old.

Yes, the foam expands over the next 24 hours or so. Plan on it oozing
out all over. After it's hardened, I trim it with a steak knife, or
utility knife. Paint it, if exposed to sunlight.

One friend foamed around his storm door jamb. The expansion was such,
that the storm door didn't close after that. The jamb pushed in.

..
Christopher A. Young
Learn about Jesus
www.lds.org
..

On 9/18/2013 2:48 PM, DerbyDad03 wrote:

I agree with everything except for your first comment. I've used unopened
cans of Great Stuff at least a year after they were bought with no
problems. Perhaps we need to know your definition of "in advance".

I don't know about the rust prevention, so I'll take your word for it.

2 other tips:

1 - You'll need less than you think to fill a gap, it will expand beyond
the opening. Expect it, embrace it.
2 - Don't put your window or door trim back on for at least 24 hours. When
#1 happens, it'll ooze out from behind the trim and be a real pain to clean
up. BTDT