There's a timestamp by default in the link table so how about adding a new column called "Expires" and adding this to the add form (maybe use a select list of days eg... 1 2 3 4 5 6 7 8 9)
....then you can insert it into the Expires column.
Then set up a script by cron to check if the current time is greater than (Timestamp + (Expires * seconds in a day)) .
...if so it has expired.
....then you can insert it into the Expires column.
Then set up a script by cron to check if the current time is greater than (Timestamp + (Expires * seconds in a day)) .
...if so it has expired.