In these cases the phrases are being used as proper nouns for preexisting events on the timeline. For example, I wouldn't say that I went for a walk "five minutes before the noon," I'd say "five minutes before noon." They're speaking in a jargon that treats these events the same way that you or I would talk about Monday or midnight and which also gives them precise meanings. If the main engine shut down on its own at an unexpected time then you could say "shortly before the main engine shut down." This lets you say things like "The main engine lost power 30 seconds before main engine shutdown" and be only slightly confusing rather than nonsensical.
