Each "week" is 3 days. On the first day of the week you play league games and the last day you play a ladder game. The day in the middle is free for you to play scrimmages or tournaments, once those are running, or to take a break and scout your next opponent. So basically you end up playing 2 games back to back followed by one off day.
League games are generated in full at the start of the season. Ladder games get generated on the fly each week on the first day of the week, since ranks change when you play, and your opponent is based on ranking.
Also, the league schedules were just generated, so check it out!