Looking at its inner working seems it's uses SQLite as storing. While a few hundred entries in any SQLite DB should be a breeze to parse and show under a second, maybe the person(s) involved in this project are not that DB proficient and made some rookie mistakes. Maybe they'll notice this and improve it's history speed as well, shouldn't be a problem for any SQL developer with a bit of experience in hands.
Looks like my delay happens when converting between units. It's almost like it prompts me to confirm when I press Enter so I end up having to hit it twice. Other than this it is really great.