My guess right now is that it could start after Trump's "15 days to stop the spread", if he declares a complete shut down of sorts, or if that's when the internet goes down completely (or maybe only social media and news sites).
That would mean the 10 days would start on the last of March of first of April, just in time for the 10 days to end on 4/10/20, which Q might have been predicting as a day of importance in posts like #500.