I created a 12 team fictional league (2 leagues, 6 teams in each). I made a custom 16 game schedule for the league that I'm able to import with no issues. The league is set up so that only 4 teams make the playoffs. My problem(s):
* I didn't add any bye weeks but the game has tacked on a bye week at the end of every teams schedule. Not a big deal but...
* My week 16 falls on 12/15. Then every team has a bye on 12/22. However, the next game (round 1 of the playoffs) then takes place 6 weeks later on 2/1. And then (and I'm not 100% sure about this but it definitely looks like it), it seems that the championship game takes place the same day as round 1 of the playoffs. At least, the date in the upper left corner of the screen does not change as it still shows "2/1".

Is there anything I can do to manage the dates for week 17 and/or the playoff games?

No, the calendar dates for some of the stages are hardcoded.