INSERT or UPDATE row to be Now + # Days
Now() + INTERVAL $no_of_days DAY,
Some of the values you can use:
DAY
HOUR
MINUTE
MONTH
SECOND
WEEK
YEAR
Update a DateTime with a random value
SET LastActive = NOW() - INTERVAL ROUND(RAND() * 72) HOUR WHERE
Feel free to comment if you can add help to this page or point out issues and solutions you have found. I do not provide support on this site, if you need help with a problem head over to stack overflow.