NEW YORK — A calendar quirk this year and Amazon’s seven-days-a-week delivery capability are building pressure on retailers to deliver. With Christmas on a Monday, most retailers have one less day to get packages delivered on time. Some are pushing up their deadlines for standard delivery or free shipping. And after promoting the convenience of buying online with store pickup, retailers are also trying to satisfy lots of customers coming in to collect their orders. It’s especially important for retailers to hit the mark after some missteps earlier in the season, and because online leader Amazon has the advantage of delivering on Sundays.