I typed =now() and I got 4/25/19 8:31, then I changed cell format to general and I got 43580.3552
My question, how can I get 4/25/19 8:31 back (day and time) from that number 43580.3552 ? (suppose undo is not working)
They are really the same value.
It is important to understand how dates and times work in Excel. Dates are just whole numbers, specifically the number of days since 1/0/1900, and time is just the fractional component of one day.
To easily see this, enter any day/time, and change the format to "General".
So a Date/Time is just a number with a Custom Format.
So all you need to get your date/time back is just change the format to a date/time number format.