Hello.

I'm looking for a function where I can send someone a (temporary) link for 24h access to the gallery. The visitor must have access to all albums and be able to download a photo.

It is also allowed without a time lock. With time slot is only a plus.

Is there already a (similar) plugin for this?

Best Regards,

Olav

There is no function to simply send a link with the required access rights and time limit.
You will have to create a new user with the required rights.
Read https://www.zenphoto.org/news/user-rights/
If you want to set a time limit on someone's access use the user-expiry plugin.