SignageWire

This RetailWire article tells us:

A survey from M/A/R/C Research found that four out of five shoppers are satisfied with wait times at stores in most cases. But it also found that 10 percent were exasperated enough to leave a checkout line if the wait becomes too lengthy.

The online survey of 13,000 customers conducted in April found that customers are satisfied (79 percent extremely/very satisfied) with an average wait time of about four minutes or less. The only exception is for club stores, where an average wait time slightly over four minutes was deemed still acceptable by those surveyed. After four minutes, the satisfaction levels drop considerably across seven other channels: grocery, consumer electronics, department, drug, home improvement, mass merchandisers, and office supply stores.

Our take:

In Paco Underhill's Why We Buy: The Science of Shopping, Underhill found that people are pretty good at estimating how long they've been waiting on line up until about the 5-minute mark. After that, they tend to wildly overestimate how long they've been waiting. Consequently, M/A/R/C's research would seem to back up that anecdotal finding rather nicely.  A number of retailers have tried everything from new checkout schemes altogether (Whole Foods, anyone?) to "checkout channel" signage networks designed to entertain beleaguered shoppers, however as far as we're aware the 4-5 minute rule has continued to hold true.