Excel date to unix time integer or unix time to excel date.

FROM unix to excel date.
[plain]=CELL/(60*60*24)+"1/1/1970"[/plain]
From excel date to unix time.
[text]=(CELL-"1970-01-01")*60*60*24[/text]
 
where “CELL” is your excel cell you’re trying to handle.
CELL can also be replaced with the NOW() function.