Quigly is correct. Ideally, two doses 2-4 weeks apart - or whatever the label directions state - with the second dose at least 2 weeks before the 'incident'.
That said, I'd be comfortable with an initial dose, then a booster 2-3 weeks later at the time of band application.
I had another banded bull submitted for necropsy this week, with tetanus, 400 pounder about 2-3 weeks out from band application. Producer was following UofKY/KCA CPH vaccination protocols...but was dismayed to find out that the Clostridial bacterin they recommended did NOT contain tetanus toxoid...so he'd lost a pretty decent calf (and the prospect of more...) as a result.
Sounds like some of these university extension folks need to think or re-think their recommendations and start including TT in the mix. With the ever-increasing use of banding as a means of castration on larger animals(though I see tetanus in banded baby calves, too), losses due to tetanus are a clear and present danger.
Have seen way too many wrecks where no tetanus protection was provided, or a bacterin containing TT was administered at band application, but the calf lost the race between developing an effective immune response and the organism ramping up toxin production.