" God gave Moses a calendar that began in spring. (Ex 12:2) God Himself emphasized the importance of Israel’s new calendar at Ex 23:16; Le 23:34 and De 16:13. God’s calendar was for marking, and keeping, God’s holy days. Using a foreign calendar became illegal. Ignoring Israel’s new calendar could cost an Israelite their life. (Nu 15:32-35)
Yet, the Jewish calendar is not the only calendar. There are plenty of calendars to choose from: Assyrian; Egyptian; Iranian; Armenian; Ethiopian; Hindu; Coptic; Mayan; Chinese; Julian; Byzantine; Islamic and Gregorian; just to mention a few. Has the Seventh Day Adventists settled on any one of these calendars? Which one? "

― Michael Ben Zehabe , Unanswered Questions in the Sunday News