Birthdays come and within weeks they are already talking about who they will invite to their next birthday party. A year is such a long time away for little ones. It is important to provide some kind of markers to help them better understand the passage of time.
Calendars are great to use because children can see the days and mark them off as they pass. Holidays and special days are often used as markers as well because there tends to be something happening each month. If these special days are on the calendar, they can count the days until they come.
It will still be confusing for many children, but with continued practice and exposure to telling time and seeing the time written out or displayed, they will eventually become more able to use it effectively.
The confusion will disappear and the questions will become less frequent.