i got cron jobs to work by adding this to startup script (got it from dd-wrt forums. dont know what it does but it works.
Code:
grep -q "^crontabs:" /tmp/etc/passwd || echo 'crontabs:*:0:0:Contab User,,,:/tmp/root:/opt/bin/bash' >> /tmp/etc/passwd
(
sleep 60
stopservice cron && startservice cron
) &
sleep 5
done