The campus-wide e-mail policy for this year prohibits you from sending more than one announcement for an event, unless you can find a creative way around it.
I actually have the opposite problem - I need to see e-mails about events the day OF the event or I won't remember about it. Honestly I think that's the way most of the campus is, I always send things out so they will arrive in inboxes the day of the event.
I think most groups do flyer prior to sending out an e-mail. I tend to read flyers and I usually know about things in advance even if a e-mail isn't sent out.