Our company used 20 seconds per 500ft AAL. So we would go downwind for 40 seconds at 1000' assuming nil wind. That would be at Flap 3, approx 140 kts (A320). Would always have plenty of room and be well inside the 4.2nm circling area. 30 seconds downwind does seem to be cutting it a little tight unless you are going really fast, that would seem pointless though as why not be configured early.