This will expire and remove revisions that are older than the amount of time you
have set as your time span. This also doesn't have an effect on protected
revisions. When set to 00:00:00 this will never expire old revisions. The format
is HH:MM:SS. To set days, simply put the number of days and a period before
the hours section. (Ex. 7.00:00:00 = 7 days)