This looks like it would take additional research to establish his arrival date. The profile states he was at the Milford meeting of November 1639 however he does not seem to appear on that list (see History of Milford, pg 7). Later to be father-in-law John Astwood does appear on that list. The "after planters" all seem to arrive 1645 or later.
Anderson profiles his father-in-law in The Great Migration Vol I:93-94. Here he gives the birth of Hannah as "say 1636." On what is Stephen's birth of 1622 based? Stephen is given a plot in Milford in 1646 but does not settle there until 1658. I haven't yet found other references to him in Anderson's work or newsletters.
Btw, Hannah was married three times per Anderson, which suggests she might have been considerably younger than Stephen. The third husband does not seem to be mentioned on her profile.
It looks like the Freeman Genealogy linked from the profile is being misquoted in the first paragraph of the profile.