NOW

Returns the computer system date and time. The value is updated when you recalculate the document or each time a cell value is modified.

This function is part of the Open Document Format for Office Applications (OpenDocument) standard Version 1.2. (ISO/IEC 26300:2-2015)

NOW()

NOW is a function without arguments.

=NOW()-A1 returns the difference between the date in A1 and now. Format the result as a number.