The Guardians minicamp is supposed to start in the first week of December and run for two weeks. From the 4th till the 19th.
The location that was recently revealed in a Janet Duch interview is Superdome Sports in Waldwick, New Jersey. It’s an indoor and outdoor facility. I suspect that the league will make it official soon. Here is a passage from the Superdome website mentioning the Guardians use of their facilities.
The Superdome is heated in the winter, and air-conditioned in the hot summer months, making it the perfect place for your training and other field needs. Our Facility is host to the most premier sports organizations in the country including New York Redbulls, NY Giants, World Class FC, PASCO, Arsenal Soccer, NJ Stallions, NY Gridlock, NY Guardians, NJ Crush, Premier College Combines, USA Field hockey, USA Soccer, NYSCL PDP, Super60 and many many others. The Superdome hosts more than a dozen large college combine and showcase events each year in different sports, and host a range of corporate events for customers of all business sizes.