While the know how on manufacturing monoclonal antibodies is high in the industry, transferring a technology to a new site and manufacturing can still take about a year. Companies have fast track designations for the critical projects, just like FDA, and so it could be done even sooner (6 months). But I imagine that the vendor wouldn’t want to go straight into developing the drug in a 20,000L bioreactor without having first assessed the manufacturability in smaller scale. In any case, it’s a lengthy process, and susceptible to human errors, especially around the tech transfer part.