On 'License' admin screen Confluence does not show expiration date. Instead it shows count down time to license expiration in form '3 month 23 days 8 hours'.

This countdown is calculated incorrectly. If you add current time with countdown value, you will not get license expiration time. The root cause of the problem is the way how Connie calculates the difference:

If subtracts current timestamp from license expiration timestamp and tries to convert this to month assuming there's always 31 days in month. The problematic method is com.atlassian.core.util.DateUtils#dateDifference is used in ViewOrUpdateLicenseAction#getExpiryTime.