Hey Funora - I’d just assume a similar amount of time as the Steam process and run them in parallel, it’s not too different and if you have all the correct information to hand. It’s quite automated so it shouldn’t be a hurdle for you if you have the company set up.
In regards to shipping on Steam or Epic, I think it’s best to ship on the platforms you know you can support as every platform is a chance to find new players interested in your work.
The Epic First Run program might also be worth checking out for you: https://store.epicgames.com/en-US/news/introducing-the-epic-first-run-program