How much time does a video game journalist even spend on one game?

Getting coverage for an indie game is different than AAA, in that it's really hard to get coverage as an indie, and when you do, they often just cut and paste your press release or press kit, and literally never install your game.

Do videogame journalists even have the time to appropriately test games in which the lore and atmosphere is delivered by scattered bits of information, like e-mails and notes?

They're busy and they need to write articles that are going to appeal to their audience. If your game gives them an easy win that appeals directly to their audience, you may get them to play it and write an article. In general, for all games, the answer is that they don't have time to play your game, and especially they do not have time to absorb your atmosphere.

How much time does a video game journalist even spend on one game?

The least amount of time they can and still do their job. Unless they really love your game, it is literally work to them, and they've got more games to play for work too, so they want to get it done as quick as they can; like any other job.

all the information you can find in there. I think that's rather doubtful, or am I just a slow player?

A game reviewer mining for everything within a game would be one that fell in love with the game. Literally no other reviewer is going to waste their time beyond what they need to review the game because they've got more work to do.

What do you think about this topic? I think getting reviews are hard enough, and focusing on building rapport and getting reviewers through several conversion processes to actually review your game is what's important. The nuance of lore building is good, but reviewers at best are only going to get the toe wet; it's up to the players to deep dive into your side lore.

Best of luck!