the XXX is the brazillian, where usually EVERYTHING down below is taken off...a bikini is more of just a "tidy up" so that when you wear your swimsuit, you're not....ummmm....hanging out all over...ummm....yuck!!!
for waxing...generally regrowth can take anywhere from 2 weeks to 8 weeks, depending on the person, the number of times they've been waxed, etc.
it might be at the lower end for the first few times, because you're hair is all at different stages of growth.
(here goes a long winded attempt at an explanation...)
there are 3 stages of hair growth. if you wax around the middle of the first stage of growth, then the follicles still have 2.5 stage of growth to work through ...even though there's no hair in the follicle, the follicle continues through the stages. if, however, you wax towards the end of the 3rd stage, then most of the hairs were going to fall out naturally anyway...a neat way to tell what stage of growth you're at is to look at the "strip" or the wax after removal. if the ends of the hairs (the ends that were inside the follicle) have little bulbs on them, then the had already lost the blood supply and were on their way to falling out already. this means that the waxing won't last as long.
it might take a couple of waxing sessions to be able to sort out when to get the waxing done so that it lasts the longest time possible.
the legnth of time a wax lasts would be the same as a threading. the reason being, the hair still grows the same way....
however, i have noticed that for women that have been waxing for years, their hair grows back thinner and softer than for someone who shaves....
hope that helps a little!