Tenet in nutshell, there is a timeline, like normal.

It’s point A in time, you perceive 30 seconds ellapsing, not it’s A + 30 seconds in time, that’s how things work.

Now if you go through that Inverting machine.

It’s point A in do stuff for 30 seconds.

Now it’s A - 30 seconds on the timeline.

There you go, Tenet explained.