The 30 minutes before rule that some impose doesn't make a lot of sense after the first few weeks, but the 30 minutes after does make sense long term.
Drinking during or soon after a meal tends to wash the food through the stomach rather than allowing it to stay there and be digested more slowly, keeping you fuller longer - this is particularly the case with the bypass which removes the pyloric valve from the system, leaving basically a funnel (pouch) between the esophagus and intestine, but still works somewhat the same with a sleeve with the pyloric valve intact. Even years post-op it is not comfortable drinking much for a while after a meal (though I may sip a bit during if something is dry.)
Before a meal with an empty stomach, it doesn't matter much whether you drink or not, as any fluids you drink flow right through fairly quickly. During the initial couple of weeks or so, you may or may not have significant inflammation in your stomach such that fluids only trickle through (if that) which is why we sip, sip, sip rather than drink normally. We want to leave some time to make sure that whatever we had been drinking has had a chance to move on through. So, once you get to the point of being able to drink fairly normally, there is little reason to stop drinking before a meal.