Since no one is replying and you are probably freaking out I'll answer. I DON'T have experience with this but I believe it's a prolapse (you are not breeding him are you?, he looks too young and too thin). I also think it is very serious and you need to see a vet ASAP. Until you can see a vet you need to keep him VERY moist and free of anything that could cause an infection. Like I said I don't have experience with this but I would imagine if you have to wait until Wednesday there is a good chance it could dry out or become infected.
I have heard of some techniques you can do to try and get it to go back in on it's own. I think one way is a sugar bath but DON'T take my word on it. Do an archive search on prolapses and you might get something. In any case SEE A VET, can you imagine how painful and uncomfortable it would be if your intestines had to hang out for a couple of days. I would actually take him to an emergency vet right now if I were you. Even if they don't have experience with reptiles, they should be able to give you some help.
Here is a link to Dr. Gecko that goes into a little more detail.
Good luck and keep us informed. Please don't wait to see a vet, it is an emergency if they don't go back in.
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0.1 Hypo Leopard Gecko
0.1 Albino Leopard Gecko
0.1 Blizzard Leopard Gecko
1.0 Albino Pacman Frog
1.0 Lovebird (Tony)
1.0 Elkhound Cross (Otto)
0.1 Malamute Cross (Paris)
6.0 Bettas