It takes me anywhere from 15 minutes to an hour for my weekly e-mails and our monthly meetings last about two and a half hours on average.
As mentioned earlier, I update them at the same time every week so they're up to date on what's happening. In fact, if they didn't make the effort to be up to date I would cut them from my Board of Advisors. I'm not sure anything really valuable can be distilled if they don't know what's happening and keep asking the same questions.