I literally have a carpal tunnel flare-up from doing so many tweaks to the GUI and the major game variables the last two days. And looking at the Game Maker load screen for 30 seconds each time I want to test a change I made isn't so fun either.
The big game companies pay guys to play their games while in alpha and beta. They explore every weird corner and combination of game events to see what happens. I saw a guy interviewed once that did that full time. He said it ruined his gaming life because when he came home from work, he didn't even want to SEE a video game.No wonder 'tweaking' has a whole other meaning to guys that don't know how to program…
A point to mention, using screen_redraw (I think that's the function anyway) you can update the in-game loading bar and redraw it in a single step. So you could load the first image, redraw the loading bar slightly bigger, then repeat.