I've been binding for a week now, and I've been using that top part of nylons. I don't feel any pain or shortness of breath, but I'm wondering if, over time, it would hurt me in any way to wear it as often as I do. I wear it about seven hours a day (So anytime I'm at school). And I mean, it is more comfortable not to wear it, but now I don't want to stop because, well, now that i know how nice it feels to have a flat chest, I don't want to go back. If this is dangerous, are there any other ways I can bind without having to come out and ask for a binder?
As long as you don't wear it for more than 8 hours, you should be fine. If you ever feel short of breath or in pain, take the binder off ASAP. Besides that, you should be okay.
Don't wear it more than 8 hours, and stretch after you've taken it off. If you can't afford an actual binder, you can use a camisole like in this tutorial: Something Incredible? If you have problems with that you can try this "adjustment": Cosplay and Randomness | Chest binding: Cami binder method (slight... Don't try ace bandages or anything like that, they'll hurt you. With time, binding will flatten your breasts a little and nothing more, but you can really hurt yourself if you do it wrong, so please be careful!
If you follow the general rules like don't wear it for more than 8 hours, and to take it off when you feel genuine pain, I think you should be fine. Don't do strong physical exercise when binding and sometimes stretch and breathe deliberately. A little bit of discomfort is normal but it shouldn't be excessive. If possible, you can order binders online, but if you're afraid someone might find out when it's delivered and that's not safe for you don't do so. I think if this method works for you at the moment and it's safe, then it's fine. Or you can take a look into the alternatives already suggested Good luck!
I agree with the advice the others gave. As long as you're following the standard binding safety rules, it should be perfectly safe. My other tip would be to take a day off from binding every once in a while to give your body a break, especially since it's harder to be sure that a DIY binder isn't putting too much stress on your body. Periodically take a day where you just wear a sports bra and a loose shirt so your chest isn't noticeable (my ribs need days off pretty frequently, and I tend to just wear a sweatshirt and not take it off all day).