When the janitor is leaning out of the window, his wife says she can't hear him for the TV music. The music is March of the Oysters by Barry Gray and this means that she is watching an episode of Stingray.
This is the first episode where Thunderbird 5 is named as such. Prior to this it is referred to as the International Space Station.
Since Thunderbird One and Thunderbird Two are used on two separate missions, their customary launch sequences are shortened to just show the lift off.
"30 Minutes After Noon" is clearly two different stories segued together. This is because Thunderbirds was originally scheduled to be a half-hour show but Lew Grade insisted that each program should be one hour. Many episodes had already been filmed, each then had to be extended. Mostly, this was done by adding extra scenes but in the case of "30 Minutes After Noon" the entire sub plot featuring Thomas Prescott and the Hudson Building fire was added to the original story which began with the London establishing shot and the agent Southern's adventure.
The hat rack scene during the transition footage is a nod to that most famous of British agents, Commander James Bond, aka 007.