He can prepare all day and he won't be able to speak coherently for 90 seconds. That's probably where the drugs come into play.
Just look at the campaign videos he puts out. In a minute long video, there are as many as ten or more jump cuts. Which means he cannot speak coherently for that period of time. The video editor has to chop it up to make him seem as coherent as possible.
That editor should get a Tony or an Emmy, whichever is appropriate, bc that's a ton of work, making Biden seem coherent.