As to #3, I don't think anyone has said that renters, by definition, are over-entitled jackasses who destroy other people's stuff for the fun of it.
Even Brad has said that his experiences (in re: to #3) have colored his perception, but I don't think he was making a blanket statement about all renters, yourself included. Bridge, you may be the model renter - pay the rent early, keep the place spotless, turn it back over in better condition than when you moved in, and be quiet as a churchmouse so as to not disturb your neighbors. That doesn't change the fact that in Brad' experience, he has seen that a significant portion, maybe even a majority, now again *OF HIS EXPERIENCES* have ended up being over-entitled jackasses who destroy other people's stuff for the fun of it.
As to a lease - I am not a lawyer, nor have I rented a room from Holiday Inn Express lately - but the leases I signed as a tenant all gave me specific rights and privileges in exchange for my rent. One of those privileges was freedom from being intruded upon without proper notice from the landlord except in the case of an emergency. Of course, the definition of what constituted an emergency was not exactly spelled out, but needless to say, we had some recourse. State law also provided us, as tenants, with certain rights which the landlord must abide by, and Oregon is one of those states that's notoriously tenant-friendly in regards to the law.
As to the OP:
Yes, it was inconvenient for the landlord to only provide you with effectively 12 hours notice in your case. But the fact that you did not receive said notice in a timely manner does not change the fact that they did not post the notices with more than 24 hours of warning. So while inconvenient, they were still well within the terms of the lease and the law (so far as we can tell). That being said, you have fairly limited options:
1) You can just deal with it, Two 24 hour notices to enter in a 1 year period is quite frankly not the end of the world. Sorry if that sounds harsh, but that's less than a 1% rate of occurrence in a year. Yeah, it sucks, but like I said, it's not the end of the world. Additionally, your choice of living conditions (as a former slob myself, I can completely empathize) means that when they do tack up those notices, you have to clean up. That's part of your choice of living style, and can't really be helped. Again, as a former slob myself, I can completely empathize. Those marathon cleaning sessions do suck, but it's part of your decision.
2) You can talk to the management and ask for them to provide a little more notice when possible, because of your work/study/sleep schedule. Remember, they are not required to provide you with any more notice than what they did give you, and the answer may very well be no. I hate to say it, but your schedule is not their problem. As long as they abide by the terms of the lease and applicable state law. And that has nothing to do with when you GET the notice, and everything to do with when they post it.
3) You can change your living situation. While buying a house may not be feasible for you at the moment, you CAN move. Is it worth the hassle and expense of moving to avoid this problem? With no guarantee that you won't find the same problem wherever else you move to? Ultimately, that's your call.
I'm not trying to sound unsympathetic here. I've experienced much the same thing you've gone through, including the 24 hour notice that they were gonna show the place. Lemme tell ya, that was a helluva marathon cleaning session, but I knew it was well within their rights. And yeah, I was working nights at the time. 6PM to 6AM, and that shift sucked that night. But the apartment was only shown one time in the 3 years we lived there. Were there other visits for maintenance issues? Absolutely. Some of them at my request, some at their request, and yeah, some of them weren't convenient for me. And yeah, sometimes I had to take a day off from work to make sure I was gonna be there when the maintenance folks were. And yes, on a couple of occasions I did come home to find a notice on my door that they'd had to come in for an "emergency" (one of them actually was, a plugged drainage pipe was causing our sink to flood with sewage). Those are the hazards of living in rented housing. And frankly, the only way to truly avoid them is to not live in rented housing. So while the "buy a house" crowd may have seemed a bit callous, ultimately, they are right....