Sci-Fi World-Building Calendar

Hi, as a sci-fi writer, I often need to calculate extraterrestrial planetary calendars with, say, 327 days per year and 21.5 hours per day. Since this is kind of difficult for an average non-mathematician to do, I always round my alien worlds to something simpler: e.g., 300 days per year and 20 hours per day. Would it be possible to create a calculator that would allow me to enter the alien-world values and instantly have an extraterrestrial calendar? If yes, that would be fantastic. I'm sure many writers all over the world would appreciate such app. Thanks!

This is a request for a calculator left by a user.

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Creative Commons Attribution/Share-Alike License 3.0 (Unported) PLANETCALC, Sci-Fi World-Building Calendar