在mysql中更改值时获取时间戳

How can I make a "timestamp" of time when I change something inside of cell in mysql and echo it in PHP?

exemple

$Notificare1 = "<p><span>Notificare1 cell has been modified ago 2 hours / 3 depends. </span></p>";}

echo $Notificare1

I tried to make a countdown timer, but it doesn't show in the moment of changing the value.

I tried to do with SELECT CURRENT_TIMESTAMP; but it didn't work neither.