How long does it take for overworld monsters to respawn?
How long does it take regular monsters found in the overworld (i.e. things like Specters, Whopperflowers etc.) to respawn?
It depends on the monster "classification".
Common Monsters have a 12 hours respaw timer. Elite run on a daily respaw timer instead. It is also worth noticing that for elite mobs that spaw with a group of common mobs, the common mobs will also take the daily respaw timer instead of the regular 12 hours one.
This means for example that a single hilichurl will respaw after 12 hours from being slain, but an hilichurl part of a Thunderhelm Lawachurl (an elite mob) group will only respaw a day later alongside the Lawachurl.
For a list of other common respaw times you can refer to https://genshin-impact.fandom.com/wiki/Reset . https://genshin-impact.fandom.com/wiki/Elite_Enemies instead you will find the complete list of enemies that are part of the Elite class.