dry periods?

Not that I know of, but maybe there's a chapter or two who does it. Most chapters don't allow drinking on Ritual days like First Degree of Initiation, initiation, etc. Drinking on Bid Day or at all during polish week/recruitment is prohibited by Panhellenic. Other than that, it's up to the individual chapter and individual NM. You shouldn't get sloppy as a new member though - your chapter can kick you out with no warning during your new member period if they feel you'll be a standards liability in the future. Once youre initiated, you're harder to get rid of, so if you cause problems as a new member you may lose your right to initiate.