Walmart is getting increasingly serious about how quickly it can get an order to a customer’s doorstep. The number of units the retail giant delivered in less than 30 minutes has doubled year over year in the current quarter, chief financial officer John David Rainey said in a company earnings call on Thursday. The gains follow a second quarter that continued to push the envelope onsame-day delivery, with fast delivery in the U. including fashion, general merchandise, groceries and medicine growing 48 percent during the quarter. Despite itsslowest total sales growthin six years amid a pullback in consumer spending, Walmart’s online business has remained a bright spot for the Bentonville behemoth in part due to the strong delivery network.