Assuming that they are testing already, just not doing automated unit tests, then from experience I'd say the breakdown would be roughly code and people change the numbers, bit this is my best guess):

20% increase in time to start with (mainly due to having to write the tests as code, getting comfortable with the testing API etc. ... testing framework stuff).

20% decrease in time longer term (mainly due to automated tests finding bugs quicker and things like instead of having to spend a long time wondering if change X will cause problems you can just do it and run the tests).