I'm treating Medium as a long-term business plan that I'm trying to build up. I have some other part-time work helping one of my friends with his online business, but that usually only takes about an hour a day. The rest of my working day I dedicate to writing and editing articles for Medium. Over the few months I've been doing this, my routine has evolved. I'll probably write about that someday, but essentially it means I plan things well. I have different days for writing first drafts and for editing, and I have a target for how much I want to get done each day. I schedule my time in 1-hour blocks, with breaks inbetween. Whenever I have odd bits of spare time in those blocks, I check notifications and read other people's articles.
It may seem risky to put most of my eggs into the Medium basket, but my philosphy is to either go all in 100% or not bother at all. I know that only a small percentage of writers get good success on Medium, but that's true of any new business. Those that succeed are often those who really threw themselves into it.
Once I've achieved good success with Medium, I might then branch out to other things. But at this early stage, I don't want to be doing 10 things at 10%. I've tried that kind of approach before and you spread yourself too thin to get proper traction with any one thing.
I'm probably in no place to give you advice, but if I was in your position, I would plan out specific time in my day for magazine writing and Medium writing. Then I wouldn't be always having to decide what to work on. It would just be a set routine. But then I like routines and plans. Except on Monday evenings when I go to improv and all that goes out the window and I get to be silly for 2 hours.