No schedules at all, i have following this game since the release. There's no such a thing. But the dev usually update the game every 2-3 months.
If the next update isn't until like 3 months, I might recommend uploading a smaller update in the meantime. Not to be rude but I went all the content in the last update in like a week or two. However if making that smaller update will cut into this update I'll just suck it up and wait as I'd rather this update come sooner rather than later.