Hey, I have a payday 2 update and it's on 100% but says that there's still time left

How long has it been doing this?

Verify Integrity of Game Cache, maybe?

Do u see the 'writing to disc' message below the speeds?
If yes, that's normal and it means that the update is being unpacked and installed

Happens every time with Payday Updates...

It's the installation process I guess. But idk why the updates from payday 2 are doing this now, it takes more to install than to download.

It's a bug or some kind or weird unpacking thing, happens to all ppl.

100% is when the game finishes downloading the update.
The patching itself often takes even longer because (in the case of PAYDAY at least) it modifies almost ALL files.