FWIW, that's all correctly set up in the schedule file I was using...allstar_game_day is defined properly, and there's a three-day break in the action in the schedule file itself. The problem I was running into seems to be that the regular season schedule respects the start_day_of_week parameter (making the Opening Day date move around in a seven-day-window), but the ASG date doesn't, at least not after the first season.
PS: Thanks battists, replying works again.
