For me I set it up for what I want my home City to be but I leave the dive/city bezel set at the 12 for timing things. This way it is easy to return it to 12 and everything is back in align. Here is the procedure I wrote up since Ball did not have one when they came out.
This is the procedure if you wish to keep the pip aligned at the top. This way if you use it to dive you just have to set it back to the 12 when done and everything is good.
1. Set the pip at the 12 and lock the second crown.
2. Cycle the hands around until the time indicates 12 noon on the 24 hour dial for your local time zone. You may have to play with it so that it stays aligned since there is some play between forward and back on the setting.
3. Rotate the crown in the time setting position backward until it is at 12 noon. You may have to cycle it around a few times and observer the date change at 12 midnight.
4. Push the crown in one click and set date and day taking into account having to pass 12 midnight to set the current local time (If you do subtract 1 for this...Same applies for the day indicator).
5. Pull the crown out now and set the local time and screw in the crown.
Now your pip is at the 12, the day and date are correct and the hands and 24 hour wheel indicate the correct local time.
This procedure will not damage the calendar mech.
If you Check the Areas of Reference on Ball USA thread there is a procedure to navigate to the Ball online manual that is updated to support all the new models as the come out. They have a similar procedure that is a compromise so it can be used for both the Diver and Trainmaster WT. The above will work for the Trainmaster Wt except just ignore the items about the pip.