score:1
Considering the size of the 2 cities, I'd say 1.5 day and 2 nights for Bergen and Stavanger.
For Oslo, I would put in at 3 days (4 nights) as it is a bigger city with more to see in general.
I like the NY Times "36 hours in" series; it kind of boils down what to see/eat/drink in short time in a city.
https://www.nytimes.com/2013/06/16/travel/36-hours-in-oslo.html
https://www.nytimes.com/interactive/2017/06/29/travel/what-to-do-36-hours-in-bergen-norway.html
related:
http://www.thetravelmagazine.net/48-hours-stavanger-norway.html
I also suggest spending some time looking at the city's tourism web sites.