There’s nothing wrong with the word ‘when’, and many many writers, including myself, use it in the way that I’m about to tell you can distance your reader from the action and lose them a little bit; they might start thinking of cats and drop the book and look around for the kitty litter tray and never come back. I’ve just read this sentence at the beginning of my chapter 9:
“When Ulrik breathes in the taste of hot dust, he remembers where he is.” And I’ve edited out two words, ‘when’ and ‘he’. “Ulrik breathes in the taste of hot dust, and remembers where he is.”
The difference is that the word ‘when’ means the action is not happening now, it happened at some time in the past or will happen some time in the future. There’s no urgency to keep reading, it’s not happening right now, and there’s probably no dire consequences bc Ulrik is perfectly fine right now. Taking out that word ‘when’ has dropped the reader right into the action.