Amazon Prime Day is coming — it’s just that nobody knows exactly when — and anticipation for the third-annual promotional event is already building on Wall Street.

Prime Day was held on July 12 in 2016 and on July 15 in 2015, so one would expect Amazon is preparing to announce the date of this year’s e-commerce phenomenon sooner rather than later.

And that’s when investors expect a rally, according to a Wednesday note from Deutsche Bank analyst Lloyd Walmsley.

In 2015, for example, Amazon shares outperformed the S&P 500 by 6 percentage points between the day that Jeff Bezos and his team made the first Prime Day announcement and Prime Day itself.

Walmsley called the last two events for Amazon a “resounding success” and noted that media reports have even suggested that this year Prime Day will last 30 hours, instead of 24.

“Amazon is requiring retailers to hold greater inventory on hand this year to serve throughout the 30 hours, which could boost sales,” Walmsley wrote.

A representative from Amazon did not immediately respond to CNBC’s request for comment.

Most of the growth in Prime Day last year stemmed from international markets, such as Germany and France, but an extension to 30 hours this year could drive more growth in the U.S., Walmsley added.

Around 70 percent of all online shoppers have said they plan to at least browse Amazon on Prime Day this year, while more than 75 percent of survey respondents with household annual income over $100,000 plan to ring up a purchase, according to Bizrate Insights.

While many rival retailers “kept it cool” with promotions to compete with Prime Day last year, Walmsley pointed out, there’s no telling what big names like Wal-Mart and Target have up their sleeves this year to take on Amazon. For many shoppers, Prime Day has become the equivalent of e-commerce player’s Black Friday. Some even prefer it to Cyber Monday.

In 2015, Amazon announced its Prime Day date on July 6. In 2016, the announcement fell on the last day of June. Walmsley has suggested investors look for “attractive short-term opportunity” in the stock over the next few days, with an announcement looming.

Shares of Amazon’s stock closed Tuesday at $976.78 apiece, having hit the $1,000 mark earlier this year. The stock has climbed more than 30 percent in 2017 and is up about 38 percent over the past 12 months.

Amazon’s latest plans to acquire organic grocer Whole Foods have many wondering how the e-commerce giant will incorporate brick-and-mortar real estate into its operations moving forward.

While groceries might not be a selling point online for Amazon on Prime Day this year, the retailer is instead looking to market more of its own devices.

In each of the last two years, Prime Day was the largest sales day on record for Amazon devices, which include the Echo and Amazon’s Fire TV device.

“Amazon’s brilliant positioning in the dead of summer marks it as the first corporate created holiday of the year in the US,” Deutsche Bank’s Walmsley said.

Sure enough, retailers and shoppers alike will be checking Amazon’s website over the next few weeks for any deals and announcements related to Prime Day, while Wall Street waits to see if a rally materializes.

Source: FactSet