You'll be able to Plan as far into the future as you wish, but you'll also be able to keep your members from seeing planned workouts until you want them to see them.
Click on the gym drop-down menu in the header and then on "edit prefs".
Next, make sure your proper time zone is selected. You'll be able to set the exact display time. Options range from 1pm the afternoon before to 11pm the evening of.
Save your preferences to begin hiding your workouts. These preferences only apply to tracks that have been set as "hidden". You won't be able to set different release time for different tracks. To learn how to hide tracks, view Can I hide planned workouts for different tracks?