App speed, like web speed, is important.

If a shopper goes through the trouble of downloading a retailer’s app, the retailer shouldn’t have her wait more than a few seconds for it to load.

To benchmark how top retailers are doing on app speed, mobile app performance vendor PacketZoom and Internet Retailer will deliver a quarterly index ranking the Internet Retailer 2017 Top 1000 retailers, and sometimes a few other smaller retailers, in various categories by their app load speed. PacketZoom measures app speed as the time it takes for the elements needed for a consumer to start searching in the app to load. The vendor calls this time to browse. PacketZoom monitors these apps across thousands of mobile devices while connected to Wi-Fi networks. 64% of consumers launch retail apps while connected to Wi-Fi, according to PacketZoom, which is why it monitors app performance in this way.

Just in time for Mother’s Day on Sunday, PacketZoom monitored flower and gift retailers in the Top 1000 that have an iOS app. Monitoring occurred between April 24-May 4. Retailers include 1-800-Flowers.com Inc. (No. 59), American Greetings Corp. (No. 332), Edible Arrangements (No. 116), Etsy Inc. (No.22), Hallmark Cards Inc. (No. 260), Party City Corp. (No. 236), Shutterfly Inc. (No. 46) and Yankee Candle (part of Newell Brands, No. 48), plus a few other retailers, including flower e-retailer BloomThat and gift card seller eGifter.

More than two-thirds (68.5%) of consumers plan to buy flowers for Mother’s Day on Sunday, and 30% of consumers surveyed will buy a gift online, a National Retail Federation survey finds.

Yankee Candle’s app was the fastest in the group, loading in 3.9 seconds.

Chetan Ahuja, PacketZoom’s founder and chief technology officer, attributes Yankee Candle’s success to the low number of images and small file sizes on the app home page. There is a direct correlation between the time to browse and the size of the content on the page, he says. PacketZoom calculates the size of the page by multiplying the average file size by the number of images. “The higher the total content size is, the slower is the time to browse,” Ahuja says.

BloomThat, for example, had the heaviest average image size, at 248 kilobytes, however it only had three images, so it loaded in 5.4 seconds, which is faster than three other retailers in this category.

The retailer eGifter landed at the bottom of the index because it does not allow shoppers to immediately search from the first app screen. A shopper has to first tap a product category before she can browse, which adds to the “time to browse” load time that PacketZoom measures.