Yeah, I know what the label recommendations are on those vaccines... but they're old and outdated... not in step with our current understanding of best colostral immunity management practices in the dam and calf. But, the manufacturers are not gonna go back and jump through all those regulatory hoops (and millions of $$$ spent) again just to change the label to reflect that newer understanding. It's up to producers and veterinarians to update their own procedures to account for advancements.
Keep on giving them 'late' if you want, but for best colostral antibody levels, they need to be given well before that 5 week pre-calving threshold in order for the cow's immune system to respond appropriately.
That said, the rota/corona virus deal is a bit different - absorbed colostral antibodies don't really provide any protection - you need the constant presence of secretory antibody(IgA) in the gut to provide 'local' protection... and we know, from studies done back in the 1980s, that properly vaccinated cows continue to produce detectable levels of anti-corona IgA in their milk for at least 30 days post-calving(that was as far out as they tested), presumably protecting the calf's gut from infection by corona virus.
