I can only tell you how I work and not really advise you on how you should work, that is such an individual thing.
I currently have two volumes up of my Bright Morn of Issareth series. I'm working on Volume III.
Volume I went up in September and the final chapter, chapter 60 was uploaded in late October. On October 31 I uploaded the first chapter of Volume II as a "teaser" for what was to come.
Volume I was not a draft, it was the finished book, I don't post drafts.
I had already been working on Volume II while doing my edits on Volume I so I was pretty far along even though Volume II was going to be longer. So from October to mid December I could work on the volume and then calculate how much more time I needed.
I started posting Volume II Dec. 13. Because there are 90 chapters I posted about 6 chapters all at once and then one chapter a day after that. The last chapter is scheduled to post March 8. I hope to have Volume III ready to post in early April. I've also started Volume IV.
I guess, when you look at it, I leave a month between the end of one volume and the start of the next volume. I never post anything that isn't already completed so that I don't get myself in a bind should something happen in my life that I can't keep up with things.
Of course, after 2020 I really shouldn't try to hold to that because, really, who knows what's going to happen?
Hope this helps.
Write hard, write true.