I think its the actual site not adbrite who does the approving. I had one campaign wait for 3 weeks to get approved before i finally deleted it.
If it was the site I would have thought it would be a quicker process as it would be automated and not a manual approval process.
A site owner/publisher gets to approve or reject all adbrite ads. There is a little section on the page that describes the ads, and it tells you how long that site usually takes to approve an ad. On my zone it says: Responsiveness : This publisher generally approves new ads or edits in 9 hours I usually do them 2 times a day. I guess you could stay away from sites that have long approval times.