Welcome to Flyertalk Clareym, official ambassadorial welcomes will no doubt be along in due course.
I've never actually checked a bag in my numerous flights from ARN, but according to MMB for my next ARN-LHR, airport check-in opens 2.5 hours before the flight. As mentioned above, since there are multiple flights per day it is possible they may accept your bags earlier if check-in is open for an earlier flight, but I have no practical experience of it, so couldn't confirm more than 2.5 hours prior.