Q. Re question above. When exactly does one recite the blessing; when signing the contract or when actually taking possession of the property, as when moving in?

A. Birchas Habbais (24: 33) and others rule that the best time to recite the brocho is when placing the Mezuzos.

Horav Shlomo Miller’s Shlit’a opinion is that one can recite the brocho when legally the property is transferred to his name.

Rabbi A. Bartfeld as revised by, Horav Dovid Pam, Horav Aharon Miller, Horav Chanoch Ehrentreu and Horav Kalman Ochs Shlit’a