Via official press release from the Cubs, and also noted on the schedule on the Cubs website, as well as the schedule on the Pirates website and MLB's schedule of national TV broadcasts, the Cubs vs. Pirates game on Saturday, September 26 will be a Fox-TV game that will start at 12:05 p.m. CT.
That means that of the 10 remaining home games, three will be televised on national networks. This Saturday's game against the Cardinals is also a Fox-TV game that will start at 12:05 CT (Fox will also carry Yankees/Mets this Saturday), and the final Sunday game of this season, September 27 against the Pirates, will be ESPN's final Sunday night broadcast of 2015.
If you've got tickets to any of those games that currently say "TBD" for the game time, you now know when those games will begin, so plan accordingly.
Incidentally, on the final day of the regular season, October 4, all games will begin at the same time. This was a change made to avoid having teams playing on the West Coast potentially having an advantage over teams whose games were on the East Coast and might have completed play before the West Coast teams began. So, all games October 4 will begin at 3 p.m. Eastern time (or shortly after that hour as per local custom). That's a smart move by MLB schedulers. The Cubs game in Milwaukee that day (and this should be shown on all schedules) will thus begin at 2:10 CT.