My boas are very much nocturnal, which is great since I work during the day. I can therefore interact with them in the evening when I'm home!
For baby and yearling boas I feed them once a week, on frozen/thawed rats (pinky, fuzzy, etc.) of appropriate size. In other words, the size of their food shouldn't be any bigger around than the thickest part of your boas body. This is a good rule for the entire life of your boa.
Older boas get fed every 10 to 14 days, and some people feed very large boas at slightly longer intervals.
For the size of your boa I'd be inclined to still feed it once a week for a while with one weanling or small sized rat (depending on whats available to you in Sweden!). Don't overfeed, it's not necessary!
Hope that helps a little! 
Steve
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"It's not that we don't know, it's just that we don't want to care..." -Wind on the Water, Graham Nash