You can learn how to add custom start and end time to your videos in this guide - How to Use Custom Start/End Time
This video has been set to start at 01:05 and finish at 01:16 of it's original timeline therefore Allowing it to play for only 11 seconds.
Following player starts at 01:05.75.
This video starts at second 10 and ends at 15.
This shows use of a custom start/end time in a playlist of MP4 videos. The first video plays in the middle for 5 seconds, the second video for 2 seconds only.
The same can be done with a playlist of YouTube videos. First video plays for 3 seconds, the second video for 7.