As counterpoint, I did all mine at a CC, and I've been absolutely thrilled that I spent so much less money on pre-reqs. I wondered if I'd wish I had done any at the university ... nope.
This is incorrect. I took all of my science pre-reqs at the community college. (The soft pre-reqs I already had from an earlier degree, but they were offered at the CC as well.) 100% of my pre-reqs could have been done on-site at my CC.
People really need to quit throwing this out there like it's gospel truth. It is true that you need to be careful to make sure that the classes you take meet the requirements (but that's also true at the university). And you want to plan ahead and study the course catalog of anywhere you're planning to do pre-reqs. But people need to quit advising people that it's universally true that you can't satisfy the pre-reqs at a CC. The CC route may not be for everyone, but it's usually cheaper and a good option for many.
Yeah, it will take about that. It's not really dependent on how many you're willing to take at once (if you're starting the sciences from scratch) because pre-req requirements mean you can only go so fast (gen chem I -> gen chem II -> orgo -> biochem .... right there is four semesters that you most likely can't stack).
But look at it this way - the whole time you're doing pre-reqs you can be out working/shadowing/volunteering to get experience.
This might have been a bit OCD of me, but I made a spreadsheet of pre-reqs. Then I organized them by semester offered and the order I had to take them. Then I just planned my next few years. Made registering every semester a no-brainer - I just looked at the spreadsheet and took what was next. They all started in a red box and turned green as I completed them. Stupid as it is, it gave me a lot of pleasure to watch the spreadsheet go from red to green.