Help with function wording used in a date column

Hi all, I am creating a spreadsheet and need help with a part that I dont know how/if I can make work. I would like that when the current or a past date is entered into the date column, it would replace the date with 'Now', but a future date would still show the date entered. I would also like for it to auto update with the current date.

Is this something that can be done with the if function?