The eras use different chronologies of the birth of Christ. Their new years also fall on different dates, so the numerical gap changes within the Gregorian year. It does not mean living at a different moment.
It is the short thirteenth month: five days, or six in an Ethiopian leap year. The other twelve months have thirty days.
Traditional usage counts two twelve-hour cycles from dawn and dusk, approximately six o’clock. Always check which system an appointment uses; the app uses the device’s local time.
It begins on Meskerem 1, corresponding to September 11 in 2026 and September 12 in 2027. Use the converter for other years rather than extending these correspondences into a permanent rule.