Obviously, if a player has a weak internet connection, they will experience delay. A countdown might be off, a part might not have deleted in time, stuff like that. But would that technically happen with guis too? For example, let’s say I had a weak connection and I pressed a button that opens a menu. Would that menu delay, and show up late? Any help is appreciated. Thanks.
Delay can only be felt when something has to go to or from the server. I assume you mean a regular server script in something like a surface gui? Server scripts cannot directly change a screen gui.
Anything inside a ScreenGui is handled by local scripts, which are entirely run on the client. That said, there cannot be network latency from the client side. However, anything shown on the Gui that relies on server side values or remote events will certainly be subject to network latency and delays.
Short answer: no, opening GUI’s is not affected by network latency.
The client never receives the script in the first place, the fact that scripts run in PlayerGui is very likely an implementation oversight from over a decade ago
You will experience many replication issues by trying to use a server script in a screen gui. You should really just use a LocalScript and remotes