- A seven-character 'complex' password has roughly eight trillion possible combinations. Plus, you shouldn't need to change passwords that much unless your co-workers are morons (i.e., "My password is too hard to remember, so I'll just write it down on a Post-It AND PUT IT ON MY MONITOR.").
- A 14-character 'simple' password has roughly 6.45 * 10^19 possible combinations. However, without any sort of standards in place, odds are that you'll have coworkers that use real words or the name of a family member or pet. Plus, there's still the possibility of blatant stupidity ("Hi nameless voice on the phone. You say you work down in accounting and need my password in order to verify something related to my upcoming paycheck? OK, here you go!").
If you're worried about brute force attacks, go with the 14-character simple system. If you want passwords that will be hard to guess, go with the seven-character complex system. If possible, you should combine them and have a 14-character complex system (6.782 * 10^25 possible combinations; harder to guess and it'll take longer to brute force).