Best to give the clostridial bacterin containing tetanus toxoid at least a couple of weeks before applying the band, in order to give the calf's immune system a chance to respond - otherwise you're setting up a potential race between the animal's immune system and tetanus toxin production by C. tetani.
Tetanus antitoxin will provide some degree of immediate protection, but it's way more expensive than the tetanus toxoid products.
I saw 4 nice big 600-lb banded bulls(steers) down or dead and submitted to the diagnostic lab just a few weeks ago. The producer had given a bacterin with tetanus toxoid at the time of band application, but the calves developed clinical tetanus and died or had to be euthanized before they developed sufficient immunity to protect them - and they had several more affected, but wer treating them with high levels of penicillin and tetanus antitoxin - haven't heard whether those lived or died.
There's a reason why the label directions on those bacterin/toxoids recommend that you give it X number of days/weeks BEFORE performing a procedure that has the potential to set them up for developing tetanus. Yeah, I know it's 'unhandy' to have to run 'em through the chute that additional time, but with the price just one of those calves would have brought...you could probably have purchased a lifetime supply of vaccine.