My first post just stated what one "should" do. What I probably would do (and have done!) is probably develop both at the same time, using the longer time if the scenes photographed have normal contrast, and the shorter time if the the scenes were of slightly higher than normal contrast. What is important is how the negatives print . By keeping notes on the time, temperature and agitation method, you'll be able to better determine the time that you should use the next time you develop these films, together or separately (when photographing similar contrast ranges in the scenes).
If you find you are needing a 3 filter or higher for most of the negatives, then you will want to increase your development time to increase the contrast of the negatives. If you are needing a filter lower than 2 all the time, then decrease the dev time to decrease the contrast of the negative. Use the strength of the shadow detail to determine if you are exposing well.
All this is instead of doing exposure/development tests -- which are not a bad idea at all...just one I have refrained from doing these past 30 years or so...