Do custom loading screens actually wait for the game to load?

Most custom loading screens I see seem to work by displaying a gui for a certain amount of time, but some have actual percentages and things that need to be loaded.

Custom loading screens are placed in ReplicatedFirst, and when the player loads, it is inserted into the player’s PlayerGui.

My loading screen does that, but it seems to just arbitrarily wait for a set amount of time, not actually wait for the game to load.

There is a content provider loading bar, it actually shows percentages and waits for everything to load.