It is used to initialize/load some variables/objects/references that has not been initialized in this frame. Sometimes in UE4 objects need to go the 2nd or 3rd iteration to get fully loaded. Sometimes you need to get much longer delays to make sure that it is all loaded.
proper time might be when your object depends on another, and you don’t know when another object is loaded and initialized. It might be loaded and initialized after your first object. Then you need to wait for the second frame.