The author has been weirdly reluctant to support new OS features, but I've been using Day-O[1] for years, it has a customizable time format[2] that could easily

The author has been weirdly reluctant to support new OS features, but I've been using Day-O[1] for years, it has a customizable time format[2] that could easily do 8601 [1] https://shauninman.com/archive/2016/10/20/day_o_2_mac_menu_bar_clock https://shauninman.com/archive/2016/10/20/day_o_2_mac_menu_b... [2] https://shauninman.com/day-o/datetime.html https://shauninman.com/day-o/datetime.html