Hi.
I'm flying into Arlanda soon in the morning, and need to catch a Ryanair flight from Skavska in the afternoon. That leaves me with 6 hours of free time.
How much time would I actually need to get from one airport to another, which would be the best mode of transportation, and how long would it take to get there?
How long before the flight I should check in at Skavska?
Thanks
Silver
The train from Arlanda to Stockholm takes between 20 and 45 minutes (depending on the train)
And from Stockholm with the shuttle buss to Skavska will take you 1.5 hour.
I wonder if it wasn't smarter to look at one of the low cost airlines flying from Arlanda 
RyanAir is flying from Nyköping, and calling it Stockholm. It would indeed be a lot easier if you would have picked a flight to Arlanda. I don't know where you are going from here, but it is very likely that there is a budget flight to there.
This is the link for the airport, and how to get there.
http://www.skavsta-air.se/en/content.asp?area=2&id=134
The Arlanda express, will take you fast to Stockholm, you can buy a ticket when you picked up you luggage, and be on the train pretty fast. By train it is just over an hour to Nyköping, and from there you can take the bus (as mentioned on the website, see above).
Check-in time differs for each company, For Ryanair you can normaly check-in until 40 minutes before the flight. but for RyanAir flights, I would recommend getting there on time, because they tend to work with fewer people, than other companies, so be prepared that you have to wait in line, to check-in a little longer than normal.