It's a blog (e.g. https://archimodels.tumblr.com). The main diference is that your posts appear on followers feeds also.
These are two really odd design decisions for blogs and trying to read content written by experts.
From the blog view, it's entirely dependent on the blog's chosen theme. Some themes may omit dates/times for whatever reason; it's up to the theme author, and up to the blogs choosing that theme.
From the dashboard (as a logged-in user), you can see a post's timestamp by mousing over the top-right corner.