This has already been documented by another user at: https://jira.atlassian.com/browse/TEAMCAL-2729

However, that issue - and issues linked to it - were marked closed as duplicates (even though none of them were actually resolved).

Team Calendars version 5.1.7 upgrade resulted in our custom date (only) fields being displayed as date/time fields. The default times were 6:00pm to 6:00pm for a full day event (all of ours are full day events because they originate in date only custom fields.) This addition of a time was shifting the display of date ranges by a day.

I downgraded to 5.0.5 and the problem went away - but eventually we will want to upgrade.