Content item preview is present before its addition.

Steps:
1. Create new LP.
2. Add Schedule block.
3. Add item (Now).
4. Move slider few hours to the future.
5. Remove item.
6. Move slider few hours before Now (notice preview is visible).
7. Remove item.
8. Check timeline markers and Full list entries.
Actual: Timeline marker is added right after addition marker, different removal time is displayed in Full list than actual (9:21 vs. 14:05)
Expected: Preview is not generated before addition time and it's not possible to remove item at that time.

Remarks: Please see attached.
On v1.7.4 the result is slightly different - there is only one item in history on Full list (screenshot 2).