Can only find this bit
Availability of the MATZ Penetration Service
3.1 A MATZ Penetration Service will be available during the published hours of watch of the respective ATS Units. However, as
many units are often open for flying outside normal operating hours, pilots should call for the penetration service irrespective of the
hours of watch published. If, outside normal operating hours, no reply is received after two consecutive calls, pilots are advised to
proceed with caution. Information on the operation of aerodromes outside their normal operating hours may be obtained by telephone
from the appropriate Military Air Traffic Control Centre:
(a) North of 5400N - Telephone: Scottish ATCC (Mil) 01292 - 692281.
(b) South of 5400N - Telephone: London ATCC (Mil) 01489 - 612406.
4
Which doesn't actually state that a Matz is closed during non op hours, just that the ATS unit may be closed.