No you don't need a prescription for hydroquinone unless you're getting the 4% version. The most common in stores is 2%, and if you look hard enough, you may stumble across a 3% version. And as for how fast it works. Well it depends on the individual. Some people may see results within a week, and sometimes it may take up to a month. I have been using a cream with hydroquinone AND aha's, and I noticed improvements within a week.
Also, hydroquinone does NOT kill off the cells which make melanin. It just turns them off. That is why it is a MUST, I repeat, a MUST to wear sunscreen while using hydroquinone. Yes, some come with sunscreen in already, yet they never tell you the spf. So always dab on your daily spf on top of the cream.
If you don't wear sunscreen, then you're not helping the problem. You will either wind up re-darkening your marks (if you got them to lighten), or you will not see any improvement at all. SO make sure you where sunscreen.
Also, if you are looking for hydroquinone in stores, it is available in your local supermarket and/or department stores (ie: Wal-Mart, K-mart, Target, etc.) Just look in the ethnic, body lotion/cream, or acne med aisles and you will run into it. ..It is usually labeled as being a "whitening, lightening, brightening, bleaching" cream. That's probably why a lot of people don't know what "hydroquinine" is. It is usually in these products. Just check the ingredient label.
Well sorry for the rambling. I am studying for a class, and wanted to take a break heh. Well good luck!
p.s. Almost forgot. Just apply the cream to the MARKS. Not your whole face. ^_^