1. Doesn't seem to support area conversions (tried 400 square meters, 400 m^2, and abbreviations in between).
2. If I only give a time, it would be more useful if it gave a time-only result rather than defaulting to the current date - unless it rolls over to a different date. (E.g. in Soulver, "2:30pm + 20hr" gives "Tomorrow at 10:30".)
3. It would be nice to support multiple abbreviations for minutes (mn/min are both used in various countries).
1. "square" before a unit I probably will implement that in the future. I'm not sure why "400 m^2" isn't working for you, I've just tried it and it works as expected for me?
2. It's a little bit clunky, but I decided to always specify the time and date being shown because there's so much potential for ambiguity. I might revisit this if I can think of a better way of doing it that's still unambiguous (the Soulver way isn't bad tbh)
3. "min" is supported, I've never come across "mn", do you know where it's used?
... works for me.
Re dateless times, yes, I think the Soulver way is unambiguous but still human-friendly.