As a rule of thumb, you should weigh yourself on a weekly basis on this -- or any -- diet. Weight varies from day to day for different reasons, so weighing yourself more often than that won't give you realistic results.
I found this out from experience when I used to weigh myself daily. I'd get discouraged when I would weigh more one day and less the next and then more the day after that.
I would think, what's the use if I gain weight so quickly? I later learned something as simple as water retention (nothing to do with my diet) could cause such fluctuations.
Dr. Agatston recommends a weekly weigh-in on the South Beach Diet. I will add that you should try to weigh yourself at the same time of day to be most consistent.
Your weight can also vary throughout the day. So, you could plan to weigh yourself every Monday morning upon waking. There is simply no need to weigh yourself any more often than that.
Another good way to measure your success with the South Beach Diet in particular is to pay attention to how your clothes fit. You will probably find your waistline has decreased after the first two weeks (belly fat tends to go first during Phase 1). See, the scale isn't the only way to keep tabs on your progress!
So, instead of hopping on the scale too soon, or too often, you could always try on a pair of jeans and see what happens!
Good luck with your continuing weight loss efforts! Thanks for writing in.