My excel keeps treating my numbers that i key in as the date even after custom formatting it to mm:s

WQR123 Dates and Times are closely related in Excel. The first day of it's internal calendar is 1 January 1900. One day = 24 hours = 1440 minutes = 86400 seconds. A duration of 5 minutes equal 5/1440 of one day i.e. 0.00347222 days. When you just enter 5 and format it as m:ss, Excel sees it as 5.0 days or midnight on the 5th day of its internal calendar. The formula bar will display something like 05/01/1900 00:00:00 (if you have a European time format) and the cell will display 00:00:00.

So, it's all about understanding how dates and times work in Excel. More about in the link below:

https://www.myonlinetraininghub.com/excel-date-and-time