The sign spoken of in Revelation 12 appears in the sky upon the 23rd of September 2017.
Daniel 12:10-12 says
11 And the time that the continual (calendar of weeks) shall come to and end, that detestable thing which stuns, stupefies and makes desolate which is delivered up, there shall be one thousand two hundred and ninety days.
In Leviticus and Numbers we read of the day of Pentecost. Some say it is 7 weeks + 50 days. Others say it is the day after the 7th week. Personally I wonder if it should be interpreted as from the 7th Sabbath to the 50th work day, which would make it all fit?If this was the case, 1335 days from the 23rd of September 2017 brings us to the 19th of May 2021 which in some locations is the Sabbath day, but in other locations the Sabbath day is the following Gregorian day.
It would be seven Sabbaths complete or 50 days (not including new Moon days).