Guys maybe I'm just dumb but why couldn't the captain of the ship have exploded it at the second she decided to? Like why did she have to slow-time it? She would've died anyway, taking the creatures down with her. Help me understand
Thing is, the auto destruct sequence was absurbly long, if she put it in place three years before and it's still going on by the time Donna and the Doctor come around. + the fact they could hear the count down going in the time they were there (a few hours) It has been a very long count down.
The Not-thing, said it themselves, they don't know slow, they don't undertand it. If the cap hadn't slowed the count down, the time it would have taken for her to get out and die would have been long enough for them to stop it. Because they supposely had copied her enough already and would know what she knew, and so would have been able to stop it. So she had to slow it down enough for them not to notice or know what it was. Dying then would ensure they wouldn't ever know.
auto destruct are never intantaneous because you need to be able to stop it, so we can suppose the normal auto destruct was just long enough for the not-thing to be able to disable it. that's why she had to slow it down and make it longer.