[frutiger]

> If it were just spelt "det" I feel like it'd have a more prominent t sound.

In other examples, the prominent “t” sounds and the vowel seems to vary based on emphasis. Compare:

1. Marriage? We only just met yesterday!

2. I’m not really sure, I think I met him four or five years ago.

[inciampati]

How are these different? What is changing?

[CRConrad]

The word "met" is first more, then less emphasised. As I understood the GP's point, it was that the more "explosive" emphasis on the whole word also changes the quality of the final 't' to a harder plosive than the relatively softer one in the sentence that is more about exactly when it was.