Perhaps this is an application for /usr/bin/batch? @reboot batch -f /etc/fortnightly now + 1 hour
Could it be beneficial to break up /etc/weekly into separate tasks, where the parent script can tell when each task last completed, and only re-run a task if it's been 6+ days since that task last ran through to the end? I've used $RANDOM in similar cases to what Lars Nooden discusses, and also like his suggestion to check 'apm' and not launch housekeeping tasks when solely on battery power. Kevin