Mike Lang's "Grand Prix," Peter Higham's "International Motor Racing Guide," and David Hayhoe and David Holland's "Grand Prix Data Book" all credit Phil Hill with fastest lap in 2:27.1 secs.
However the September 1961 Motor Sport report of the race credits Moss with fastest lap in 2:30.4 secs on lap 2, which "DSJ" expresses surprise at.
On balance, 2:27.1 sounds the most plausible.