Most podcast platforms require at least one published episode for your podcast to be listed. And when you initially submit your podcast, it can take several days for it to be published in various directories. This is obviously suboptimal if you want to make your first episode available at a specific time. But there is a trick you can use to better schedule the publishing of your first episode:
Simply produce a trailer for your podcast, which you publish as episode type "Trailer" and as episode number "1". Now your podcast has a first published "episode" and you can upload it to all directories. When you go online with the first real episode, it will only take a few hours until it is live. That's much better for planning your first big gig, isn't it?