About this detail of the Tiger
A surviving German drawing  shows how to upgrade an old Tiger. When it was drawn, it specified an upgrade to the second kind of firewall vent. But later the drawing was altered to specify this third kind of vent. So we know this vent was introduced no later than the drawing change, 6 March 1944.
A possible date for the introduction of this vent is September 1943, when the entire firewall was simplified [1, see 22.214.171.124] .
At some unknown time the clutch control lever was deleted from the HL230 engine. A new device, the cold-weather starter, was added in its place. This device had a thumb lever, visible at the bottom of the photograph; so the firewall door remained.
This door had a rubber seal around the edge. Since this door was not spring-loaded, the crew could simply leave it open if they wanted hot air.
The same kind of vent is found in the surviving Sturmtiger at Munster museum. This photo  , taken from underneath, shows the catch for the door.