Does "av og til" mean something like "from time to time"? It looks a bit like German "ab und zu" but I can't catch the meaning of "now and then" :)
No, this is a set phrase. Av og til means "now and then". You have to translate the whole phrase in one go, not word by word.
It might make more sense if you think of it more as "off and on" than "now and then" but neither are a direct translation.
Seems like the closest literal translation is the English phrase "to and fro", which doesn't fit perfectly but it's pretty close to "here and there", which would work in this sentence. Even though "here and there" is literally about place and not time, it is commonly understood in a time sense via metaphor.
I'm one of the incubators, meaning I can edit the course, and look up alternate answers when there are questions like "can I say so and so?".
When you get Jeg jobber av og til and Duo wants you to fill in the English response, those responses have been added manually by a team of people. There is a preferred answer, in this case "I work now and then", but there is also a number of alternatives that we have to add as they are not incorrect (synonyms, ambiguous meanings, set phrases with no exact translation, verbs in present tense, adding hints (mouse overs).. etc). Sometimes a translation can be a bit unnatural as it may be more important to show the relation between the words, than getting a nice flow. Stuff like that and a whole lot more. I'm a fairly recent addition to the team, and I was surprised by the complexity of making this course!
I can't answer for other dialects, but in most flavors of American English "sometimes" and "now and then" are not entirely equivalent. "Now and then" implies that the activity is intermittent, not just that it's part-time.