@HeathrowAirport
Just settled into the initial cruise attitude is also a likely time the cockpit door opens for many reasons, such as refreshments, dinner order taking and toilet rest etc
If someone says this is not a possibility, then you clearly are a wannabe.
MAS370 reached 35,000 feet (which I assume was its TOC that day) at 17:01 UTC,
well 20 minutes before the last blip reported by FR24 (17:21 UTC).
I assume that 35,000 feet was TOC for that flight because the altitude did not change for 20 minutes. However, having tracked the same flight on FR24 the day after and yesterday, I noticed that TOC was 37,000 feet.
I guess only the airline may provide further information about this.