Was the Montauk Long Island facility used for time travel experiments in conjunction with extraterrestrials?

This is indeed the case. There have been a number of such forays. In fact, the Mercenary Army Program recruits undergo time travel as a routine for a variety of reasons. The whole 20 and Back program is based on this use of technology. All involved are aware of this capability. It is still under control of the extraterrestrials and being jealously guarded.