No one here is a vet. You can get a lot of advice here, but I would not go seeking or following advice on dosing or prescribing medicine. If someone came on here and advised that skipping a day was acceptable would you really follow that advice? I sure as hell wouldn't.............
You can't always compare dosing rates between species. Different species metabolize medication at varying rates. Your vet prescribed a specific dose and frequency - I would stick to it unless he advises otherwise.
I find it hard to believe that the vet's office can't take and return a simple message.