My spleen has been enlarged for over four months now. I've been checked out fairly thoroughly and the best guess at this point is from the EBV virus. The hematologist I have seen said it can take awhile to reduce, which is what my primary also told me a couple of months ago. Each person is going to be different, but my guess is at least 1-2 months is needed for reduction, if not longer, such as in my case.
Just be careful with it. My hematologist told me to avoid contact sports and heavy lifting. Snowboarding is not a contact sport, but if you take a bad spill you could risk rupturing it. You need to talk to your doctor because a ruptured spleen is a medical emergency.
Every person has a different story. I know someone who still has an enlarged spleen, even though it has been months.
I would call your physician and talk to him or her before you take your trip.
Good luck !