Sorry to give you bad news, but expressing it without QT is most likely going to cause the loss of the eye and a quicker infection to the rest of your fish. Antibiotic treatment is about the only fix I know of, but the good news is that I know it works because I had the same pop-eye problem with my Koran Angel and the good folks at Texas A&M University Veterinary Hospital (shameless plug) helped me out.
Causes are typically trauma resulting in an infection that builds up behind the eye and pushes it out.
Mortality rates are pretty high without treatment and it kills pretty quickly (couple of days). Sadly, if you cannot QT and treat before Wednesday, my recommendation is euthanasia. I know, I know, many will not agree with this for ethical reasons, but the likelihood it will spread to the rest of your tank in your absence is high.
Maybe you have a friend with QT capabilities???
Sorry!!!