When creating periods in a maintenance period please provide "end date" calendar rather than days, hours, minutes etc...
Current the actual maintenance period has two calendars for "Active Since" and "Active Till" which is very easy and only requires selecting a calendar.
When entering a period it only has "Date" as a calendar and "Maintenance Period Length" where you have to select days, hours and minutes.
This requires you to count what is required until the end date rather than just selecting end date from a calendar.
This will help when creating a period and also checking the actual date where the period ends after the fact.