Possible Clues:

• Sched. uncertainty
• Not yet known (Abbr.)
• Not yet settled, briefly
• Not yet figured out, for short
• 'Will send details soon' (Abbr.)
• 'Hang tight for details' (Abbr.)
• Not yet decided, briefly
• 'Don't know the details yet' (Abbr.)
• Initials of uncertainty
• Schedule placeholder letters