Q. This year (5781 – 2021) the first day of Rosh Chodesh Adar will be’H be on Friday. Does Mishenichas Adar Marbim Besimcha, with all the segulot begin already on Friday since after all it is still the last day od Shevat. This makes a difference in my case for signing an investment contract that has risks and can use all the great mazal of Chodesh Adar.
A. On question 1634 we mentioned that Adar is a time when good mazal prevails, so it is a propitious period to begin new shiurim, establish new mitzva projects, and other endeavors whose success will bring joy. (See question 990 regarding new business ventures).
Indeed, on the first day of Rosh Chodesh Adar the date written on a Halacha official document such as a Get, would be; ‘The thirtieth day of the month of Shvat, which corresponds to Rosh Chodesh Adar.’
Nevertheless, Horav Shlomo Miller’s Shlit’a opinion is that it is already included on the auspicious and fortunate good mazal of Chodesh Adar.
Rabbi A. Bartfeld as advised by Horav Shlomo Miller and Horav Aharon Miller Shlit’a