Using /schedule function namespace:path <time> to schedule a datapack function for later execution executes the function immediately, if executed in a dimension other than overworld (tested for nether and a custom generated dimension)
This bug apparently already existed in 1.16.1 (see https://bugs.mojang.com/browse/MC-196949)
To replicate, add the attached datapack to your server, reload and go in the overworld dimension.
Then execute the command "/function bug:test".
After 3 seconds, the text "test" will be printed in the chat.
Now go in the nether and run the command again.
The text will be printed immediately.