Hi another college student here, thought I'd just drop some info about general community colleges in the US and what not.
-So yes for full time most colleges require a person to take 12-13 credit hours a semester. Each class depending on what it is, is a different amount of credit hours. For example my Intro into Biology course was 4 credit hours, as most science classes tend to be at least 3 hours long (so there's time for labs) they're worth more credit hours. On the other end just about all my other classes tend to be an hour 45 to 2 hour classes and are worth 3 credit hours. There's also sometimes special classes offered outside the normal basic courses that can be worth 1 or 2 credits, like an Intro into College course I took my freshman year. Those tend to be shorter and have odder schedules (my class would meet every other tuesday & thursday). So even though 13 credit hours sounds like a lot, it's actually just 4 or 5 classes a week to be full time.
-Regardless of major every college requires you to take a certain amount of core classes like math, science, English, foriegn language etc. I'm currently an art major and in order to complete my degree i've had to get 6 credit hours in a foriegn language, 9 for English, 8 for science, 3 for math, and so on and so forth. While there's no one saying you have to get your basics out of the way the first 2 years of college, that's typically what a lot of people, myself included, do. So in the basic courses you can end up in classes with people of all sorts of majors. In your major specific courses you probably won't see too many people outside your major unless it's like a basic course and they needed another random class in order to be full time & not lose scholarships, or if the subject just interests them. There are some courses that are only open to people in the related majors, these tend to be the more advance courses. Like Advanced Biologoy 1 & 2 is only open to biology majors. No one is forcing you to just do basic classes though, so there's the option to take some of your classes related to your major off the bat. As long as at some point during your 2 year, 4 year, etc. degree you get all the credit requirements done, you can basically kind of do what you want. The only thing is sometimes specific classes have requirements (like for my foriegn language i needed 2 semesters worth of the same language taken consecutively) or they may only be offered in certain semesters (like in my art classes I had 2 that were only offered in the fall and 2 that were only offered in the spring). Sometimes scheduling can be a bit tricky on your own, so everyone in college gets assigned an advisor who is a professor in the field your majoring in. If you choose to meet with them, they can help you figure out how many classes you want this semester, what time and days will fit your schedule, what you should take in the future etc.
-As for schedules like i mentioned above, most classes are from like an hour and a half to 2 hours, sometimes 3. There are some early morning classes that meet 7:45am at my school. Typically people who take those either: are freshman who don't know any better yet (God rest thier souls), early birds, or people who were desperate to get into a class. There are also some late night classes that are from 6pm to 9, and of course there's classes in between the two time frames. It depends on how many classes your craming in your schedule, but you can either have 5 minutes in between to get to classes or like 2 hours. Typically for days, classes are either scheduled Monday-Wednesday-Friday, Monday-Wednesday, or Tuesday-Thursday. This way the 4 or 5 classes you have gets split up over a few days, so you can end up having 2 on say Mon-Wed, and the other 3 on Tues-Thurs. This is really nice and makes the work load more managble in my opinion. Certain classes are only offered on certain days at certain times (which is why it's recommended to meet with an advisor to make sure there's no potential conflicts in your schedule).
-With most colleges there's also the option of taking online courses for your credit hours. With these classes as long as you get your assignments, tests, discussion posts, etc. in by or before the due date you'll be good. So usually the professors in charge of these will give you the dates of all the assignments ahead of time in the syllabus, and you'll be given the leisure to work on everything sorta at your own pace. I currently have 3 online & 3 in class classes, so mon-wed I literally only have 1 class in the morning, and then I have the rest of the day to work on online work or nap or whatever. Online classes can be nice, but it's easy to forget about them or just plain slack off on assignments.
-I'm not a double major myself, but I think double majoring is basically the same as a single major, but you have to take a lot more classes. I believe you have to make sure you meet the requirements that both individual courses have class wise. So say i was an education & art double major, on top of the overlaping basic courses, I would have to make sure to take my required education related courses and my art courses. At least that's what I believe, I may be wrong so it's best to do some research on that.
For anyone curious I hope this helped~ Sorry it got a bit lengthy though.