TimelessLib only does something when another mod uses it. So the right place to install it depends on the mod that requires it.
Match the mod that needs it
1. Find the mod that lists TimelessLib as a requirement.
2. Check where that mod is installed:
- Client only: put TimelessLib in your own game's mods folder.
- Server only: put TimelessLib in the server's mods folder.
- Both sides: put TimelessLib on the client and on the server.
3. If several of your mods need it, install it wherever any of them runs.
Safe default for multiplayer
The mod's description doesn't say which side it must run on. If you can't find a clear answer from the dependent mod, install TimelessLib on both the server and every player's client. A library on both sides rarely causes trouble. One missing on the side that needs it usually stops the game or the server from starting.
Singleplayer
In singleplayer, your game runs both sides at once. You only need one copy in your mods folder.
Quick checks after installing
- Launch the client and confirm it reaches the title screen.
- Start the server and read the console for errors that mention a missing mod.
- Join the server. If you get disconnected with a message naming mods that don't match, compare both mods folders and make them line up.