T.H.
Zoloft is an antidepressant that also works well for anxiety; however is takes up to six weeks at an adequate dose (100-150 mg for most people) to get the full benefit, though you could start feeling better within a few weeks of the correct dose. There is no reason to take it twice a day, and an evening dose might cause insomnia. For immediate relief of anxiety one can use a benzodiazepine (ativan, xanax, klonipin) although these can be addicting. But if you stop them once the Zoloft is working, there shouldn't be a problem.
A little about me - Psychiatrist in Palo Alto with a husband and two kids 20 and 13.