Possible Clues:

• 'Check this time slot later'
• Like wedding dates for many engaged couples, briefly
• Not yet settled, for short
• Not yet known: abbr
• Up in the air, on a sched.
• Placeholder inits
• Letters on an incomplete schedule
• 'Details to come . . .'
• Not yet certain: Abbr
• Brief "We'll figure it out later"