Yeah reading time is key. I think for Medium 3–5 minutes is optimal, with a max of 7 minutes or 9 minutes if your story and writing style is exceptionally engaging, but I think reading time is a factor in curation. My longer stories tend not to get curated even if the quality is good. Probably best to break them up into component parts in a series if you find yourself going over.
I think the ideal is to spend a lot of time researching, writing and editing relatively short articles.
The curation is done by hand but they obviously use some kind of tools to sort through the all the stories they get. I know from some of the official statements from the company that they track the amount of time you spend in the editor.
My hunch is that to identify stories for curation they probably look at the ones where writers spend a lot of time writing. That would make the most sense. Then they check for a good headline and graphic and probably only skim the content itself.
The best tip, in my opinion, is to be a good self-editor. Before hitting “publish” see how long your story is in minutes and then go back and look for places you can cut. A lot of times, I think we fall in love with our own words and don’t realize often how useless many of them are to the overall story.
Nine times out of ten, cutting out all that dead wood will make your story more readable and improve the likelihood that the reader will make it all the way through to the clap button.
You can also let inline links do the heavy lifting instead of explaining every unfamiliar term or reference in the story. I cut out a few hundred words that way.