220Kt is specified at MAY because that is the speed on which the hold is based.
The latest PANS-OPS (4th) edition specifies 230Kt as the maximum holding speed for CAT C+ holds.
This hold is probably based on the old criteria of 220Kt so hence the specified limit.
So even if there was nothing specified at MAY one would have to be 230Kt or less by then.
Heathrow require that any aircraft unable to accelerate to 250Kt after noise abatement procedures to notify ATC. They say that poor speed performance can result in a delay.
Therefore ATC are expecting 250Kt after noise unless told otherwise.
That would make it - noise procedure, accelerate to 250Kt then decelerate to 220Kt by MAY.