[DS-805] Fix the end time of the demo events to display the correct duration information in the schedule.

[aleevas]

Related Issue/Ticket: DS-805

Steps to test:

• [ ] Run migration with Virtual Y Demo content
• [ ] Go to /virtual-ymca?check_logged_in=1#/schedule
• [ ] Verify that events in the table have the correct duration information.

Quality checks:

Please check these boxes to confirm this PR covers the following cases:

• Maintaining our upgrade path is essential. Check one or the other:
  • [ ] This PR provides updates via hook_update_N or other means.
  • [ ] No updates are necessary for this change.
• Front end fixes should be tested against all of the Open Y Themes.
  • [ ] Tested against Carnation
  • [ ] Tested against Lily
  • [ ] Tested against Rose
  • [ ] This change does not contain front-end fixes.
• [ ] I have flagged this PR "Needs Review" or pinged the VY devs/QA team in Slack