The decrease in spawn timers is because of night time. Monsters will spawn near instantly at night, and keep harassing you forever. More if you're doing noisy activities like chopping wood and building.

Creatures in valheim aren't dumb, if you make noise they WILL come to greet you with a pointy appendage/stick/weapon.

Flat open spaces also lend themselves to this, low height mountains and plains often spawn creatures nearly instantly as you kill them.

If you are talking about mobs respawning during a raid that's programmed behavior. When you kill one of the raid creatures a new one spawns at the center of the raid circle and will run toward the player if the player is inside the mob's perception range.

As long as the raid is active, killed raid mobs will respawn until the raid ends.

Yesterday, I died because I charged at a body pile in a draugr village. I killed the elite draugr who was there, and draugar start spawning one after another after I killed them and before I could destroy the pile, like skelettons sometimes do at evil bone piles.

There were spawning sites with a very short respawning time already. Did they adjust these times too? In my case, it is possibke that it was only a short-time spawner (and also a high-level one, as it can spawn elite and 2-star draugar), already before the recent updates.