Enoch’s year had 364 days. There were 90 days in each of the four seasons + four additional intercalary days, one each for the: vernal equinox, summer solstice, autumnal equinox and winter solstice.
Please read this article for a much more detailed explanation: https://1260d.com/2019/06/27/archangels-assigned-keep-orderly-cosmos/
3.5 years would have 1274 days. The Revelation 12 sign on 23 September 2017 plus 1274 days will be 20 March 2021 – the vernal equinox, or first day of spring.