I think buying tobacco can be done with equal success any time during the show. I don't think the prices drop. However, if you want to discuss blends, you might try for calm times, perhaps early and in the doldrums after lunch. For pipes, late in the last day is often opportune, when sellers are faced with the prospect of hauling their wares home. You won't have the fullest selection, but you might find some generous discounts. The late great North Carolina pipe carver Bob Hayes sold me my only bamboo shank pipe, a Dublin, for what could have been a half or third of the original price in the last hour of the TAPS/North Carolina pipe show.
A few other suggestions: Have a plan in mind and stick to it, in terms of what you want to buy and on what budget. Pick up business cards for further follow-up on things you like but didn't plan to buy. Engage in conversations during slow times -- you can learn a lot. Be polite about negotiating; people don't mind hearing an offer, but be polite.
