I guess will be pretty hard to make any1 to get real interest to help you out,
by posting your whole code in 1 huge line w/o knowing where each code line ends!

Also, @ line #7, I don't think (time / 5000) will have many chances to be exactly 5.
Perhaps you've meant the rest of the division -> (time % 5000)?

I believe the easiest way to control your program for such issues is to create program state variables.
Like, a state for stateLoading, stateWaiting, stateDisplaying, stateRunning, statePaused, etc.

1. void loadScreen() {                  //Code to load start screen
2.   if (millis() - time >= wait) {
3.     time = millis();                      //also update the stored time
4.     image(loadingImage, 0, 0);
5.   }
6.  
   
7.   if (time/1000 == 5) {
8.     time = 5000;                         // Stop here
9.     startMenu();
10.   }
11. }
12. 
    
13. void startMenu() {                     //Code to load the real game
14.   text("Start", 350, 300);
15. }