I’ve published a substantial number of studies related to Fed Days and the action that takes place following them. Most of the studies I’ve published have only looked at scheduled Fed meetings.
Unscheduled Fed meetings have been typically been surprises where the announcement came out of the blue - and the time of day was not consistent. Monday is the first unscheduled Fed meeting that I can recall that has been announced beforehand. While behavior may fall in line with other scheduled Fed meetings, I believe it would be dangerous to make any assumptions in this unique case.
Traders should be aware that news will likely hit in the afternoon that may affect the market.