The clock is ticking for iPhone owners hoping to help pay for an upgrade by selling their old phones.

Apple announced a new version of the iPhone – the iPhone 7 – Wednesday, and resale prices for used iPhones have already started declining, according to Matthew Reardon, marketing manager at electronics marketplace Glyde.

But there’s still time to cash in, particularly if consumers reject Apple’s decision to skip the headphone jack and deem updates of a faster chip, longer battery life and better camera more evolutionary than revolutionary.

Prices typically drop about 15 percent around a new iPhone release on Glyde, with the biggest drops arriving a day or two after the announcement, as upgrading iPhone owners try to offload old devices, Reardon said. Resale prices on the iPhone 6s and 6s Plus – no longer the newest iPhones on the market – likely will take the biggest hit, he said.

Gazelle, which buys back used electronics, said prices usually drop by about 20 percent when a new iPhone is announced, with prices for the most recent model dropping by as much as $100. But if the changes are considered more modest, as they were when the iPhone 6s replaced the 6, prices likely will drop more slowly through the holidays, Gazelle gadget expert Amy Rice said in an email.

On Wednesday, several buyback websites offered between about $230 and $380 for a 64-gigabyte iPhone 6s in good condition on the AT&T network.

Demand for iPhones has slowed in recent months, and some analysts have pointed to signs customers are waiting longer before buying the latest model.

According to a May report from BMO Capital Markets, the share of iPhones in use that are more than two years old has never been higher. But analysts said they see that as a reason to expect strong sales of the iPhone 7.

All those aging devices could mean more consumers will be ready to upgrade even without a new must-have feature, the BMO Capital Markets analysts said.

But a few years of incremental updates also could be encouraging customers to settle for an iPhone that’s new to them, but not the newest.

New iPhone launches always have prompted a rush of people looking to sell older models, but in recent years Glyde also has seen spikes in buyers trying to score a deal on older models, Reardon said.

More Americans say they intend to purchase a smartphone in the next three months than last August, according to an annual survey from investment bank Baird predicting “solid” demand for the new iPhone. But among prospective iPhone buyers, 58 percent plan to get the newest model, down from more than 70 percent in the weeks leading up to the 2015 launch of the iPhone 6S and the 2014 launch of the iPhone 6.

About 42 percent plan to buy an older model, up from about 29 percent before the launch of the iPhone 6s last year, according to Baird’s survey.