1: The new SAT is not designed with time to spare on each section, but with practice most people can finish all the questions before time is called. I would highly recommend submitting a request for extra time so you can reach your full potential on the test. It may seem like a long and arduous process, but it's not fair for you to be put at such a disadvantage because of your disability.
2: The connection between SAT scores and IQ was pretty well-established before the new SAT. This is not surprising because the SAT was originally developed from an IQ test. However, since there have been significant changes to the format and content of the new SAT, it's not totally clear how the two are related now. More statistics will need to become available before any conclusions can be drawn. Also, keep in mind that both are very flawed measures of intelligence. A person's SAT scores can change significantly over time because it's possible for a person of average intelligence to perform at a high level if they've done enough prep.
3: The question of whether or not you should be happy with a 1280 depends entirely on where you plan on applying to college. A 1280 is well above the national average, so it will get you into many moderately selective schools. The only way to tell if you need to retake the test or not is to look up statistics on admitted students for the colleges you want to attend. Here's more advice on finding a good target score.