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.
Most blogs in the early 2000s evolved into longer articles; but some weblogs kept the style and evolved it into another direction, mixing short posts with links, images, quotes and such. A term for that new mixture was tumblelogs.
https://web.archive.org/web/20050722001616/http://redhanded....
https://kottke.org/05/10/tumblelogs
https://leahneukirchen.org/anarchaia/static/faq.html
http://leahneukirchen.org/blog/archive/2005/04/thoughts-on-v...
That was all 2004/2005ish, before Twitter and Tumblr. So yes, Tumblr has is original inspiration in the the early blogging scene and I suspect the name too. But you’re not wrong, another essential part of Tumblr is the builtin social network and the new mechanism of commenting and reblogging. If I remember correctly those came a little bit late.
People could do that with blogs.