Monday, March 19
Either way, he reports the following, from the Italian media..
Benedict XVI will "free" the Tridentine Mass... The Pope’s "Motu Proprio", which should be promulgated between the feast of the Annunciation (25 March) and Easter, is ready. The text is highly protected ("blindatissimo" = "very heavily armoured"); but according to leaks ("indiscrezioni") from a very good source, it ought to reverse the present situation.
I wouldn't expect it on a major holy day: B16 doesn't seem to work that way.