bk check speed

I use this in /etc/Bitkeeper/etc/config:

partial_check: yes!

But if I don't touch a repo for a while, I still have to wait for a full
check sometimes when I'd rather not.

Any suggestions for what "bk check" options I should put in cron to
a. make checking during the day always be fast
b. actually do useful checking (my desktop is up 24x7, so expensive
checks while I'm asleep would be fine)

thanks,
-Len