Rings run on two clocks: the one counting down to your proposal, and the retail calendar turning underneath it. Buyers who respect both pay less and panic less.
The lead time nobody budgets
A made-to-order or custom ring commonly takes four to eight weeks, longer near holidays when every workshop queue swells. The arithmetic is unforgiving: a holiday proposal is ordered in autumn. Add a comfortable margin for the resize you may need and the inspection you should perform, and three months out stops sounding conservative.
The sale calendar
Online sellers discount settings more readily than stones, with promotions clustering around the gifting holidays and the big retail weekends. The stone itself moves less, because certified stones price transparently against one another. Translation: time the setting purchase if a sale is near, and judge the stone on its merits whenever you find the right one.
A certified stone is a commodity with a paper trail. Commodities reward comparison far more than they reward patience.
Where haggling works
Large online sellers hold list price and compete through breadth and the occasional code. Independent jewelers have real room, especially on settings, trade-ins, and bundled services like future sizing and cleaning; a polite request for their best price, with a competitor's quote in hand, is standard practice and taken as such. Everywhere, the strongest negotiating position is visible willingness to walk.
The short of it: order with two months of slack, time the setting to the sale calendar if one is close, and save the haggling for the independents.