Assuming we are talking about boring slides with just a few bullet points, then 99% of work is actually creating the (text of the) presentation. Creating boring slides can be done in a few minutes.
Most time when I see a wrong and overful slide deck, people don't actually have any idea what they want to say. They just dumped some information in the slides that might be handy.
Most time when I see a wrong and overful slide deck, people don't actually have any idea what they want to say. They just dumped some information in the slides that might be handy.