Early was how Alastor functioned. Early was on time for him. Being somewhere early gave time to prepare, to plan, to consider how to best execute whatever orders it was that he had been given or to analyze the situation he was being placed into. Some of his people joked that there were really two times, the time that everyone else had and then 'Moody Time', which would inevitably at least fifteen minutes earlier. Really he enjoyed being the first to arrive. It meant he could take the most advantageous position and have the most time to assess risk.
As he watched Rookwood approach, he raised his eyebrow with a bit of a smirk. Despite how gruff he was on the job, Alastor could take a joke. And even if the flirting was not a joke, he really would not care. Rookwood was a good auror and that was all that mattered. As long as something like that did not interfere with their mission than he could say whatever the hell he wanted.
"Been waiting her ten minutes, Rookie." Alastor said with a bit of a laugh. "Beginning to wonder if I was going to have to hunt your arse down."