you can, but it's not easy.
put the unban date in the account notes.
{.set account|NAME|notes key=unban={.time|yyyy-m-d|offset=7.}.}
from next version, leaving empty the NAME will make it work on the current account.
then in an event
[+request]
{.if|{.and
|{.not|{.get account||enabled.}.}
|{.{.time|yyyy-m-d.} = {.get account||notes key=unban.}.}
/and.}|{:
{.set account||enabled=1.}
:}.}
this solution is UNTESTED
and will work only with next version, bearing the new {.get account.}