If you've recently removed some time slots, there's a chance there still may be a few hanging out in their previous time slot. To get these shifted into the new slots, you can take advantage of the Fill in Time Slots button.
Helpful Tip: Shuffling will only move the Pins around within other scheduled Pins and won't fill in open time slots.
To use the Fill in Time Slots button:
Navigate to the Publisher tab in the left-hand column (look for the icon of a megaphone)
2. Just above the schedule on the right-hand side, click the little button with three vertical dots.
3. Select "Fill In Time Slots" from the drop-down menu.
4. In the pop-up window, click "Yes, Fill In My Time Slots" to accept.
5. Ta-da! All unlocked Pins have now been "condensed" to fill in the first available empty time slots.