TV ad buyers are creatures of habit. Every year, they take the week after the broadcast upfront presentations to mull over the networks’ new offerings and confer with clients, take off for Memorial Day weekend and then start to get in the swing of the things when they return to the office. Upfront sales always begin in earnest in the second half of Memorial Day week, and networks and buyers didn’t break tradition this year. Speaking of tradition, as the No. 1 network in adults 18-49 for the past eight years, Fox kicked off the proceedings in the past few years. Its ratings streak ended this year but nevertheless Fox is again an early deal-maker. ABC also is said to be writing business, with the other networks also jumping in or about to do so. According to analysts, the networks will see mid-single-digit growth in upfront ad prices this season.