Before I left for Norway, I researched the internet for some practical information regarding how much time it would take for me to change from the international to the domestic terminal at the Oslo Gardermoen Airport. I was flying from New Delhi to Tromso via Paris and Oslo. Perhaps, the easier way would have been to fly directly from New Delhi to Helsinki with Finnair and then take a connecting flight to Tromso. However, I went with Air France because the timings suited me better.
Anyway, to be on the safer side so I didn't miss my connection to Tromso from Oslo, I gave myself 5 hours between arrival and departure at the Oslo Gardermoen Airport. But I did not realize that since I had already gone through immigration in Paris, I would quickly be able to go from the international to the domestic terminals in Oslo. In less than two hours, I was able to collect my bags at the international terminal, self check-in and drop my bags at the domestic terminal and go through security. To add to my dismay, my flight to Tromso was delayed by an hour which meant a total wait time of 4 hours at the airport! Thankfully I had upgraded my ticket to SAS Plus and was able to access the domestic lounge during this time. There is no walk-up entry at the lounge and the doors open with the boarding pass, so it ended up being a great idea to have this SAS upgrade done before arriving in Oslo.
For passengers flying directly to the Oslo Gardermoen Airport from the US or other countries outside the Schengen area, I recommend allowing enough time to change from the international to the domestic terminals since you will also have to go through immigration in Oslo. Also, it depends what time of the day you are arriving in Oslo. I arrived around 12 noon and there were not so many passengers. However, I noticed that it got really crowded towards the evening.
Read my post on 'Some amazing facts about Norway you should know before you visit'.