Time and date issue when importing SharePoint calendar

My company uses a SharePoint/ shared calendar for bookings of rooms and spaces. At the end of the month, we import the calendar and analyze the data. In doing so I noticed that the invisible date, which is attached to each time value was set to the year 1900. This creates a problem with timelines etc. Is there any way that I can avoid this issue in future or fix it on the current spreadsheets ? 

THANKS!