Created in broad daylight and took 20 minutes to form.

The Julia is one of the formations that has formed during the day. We know this because the owner of the field had checked his fields that morning and found nothing wrong with it. Later that day around half past five an aircraft flew over Stonehenge and the pilot as well as his passengers claim that the formation wasn't there yet. As you can see on the picture above it's kind of difficult to miss while flying over it. But when the aircraft returned at six o'clock the Julia formation was there...
This sets the timeframe in which the formation formed at 30 minutes, but there's another indication of the time in which it appeared. At the local police station of Wiltshire reports came in around ten to six of cars standing still on A303, the road overlooking the field. Before that time there was nothing unusual, but after 17.50 PM drivers stopped to take a look at the beautiful forms of the Julia. This means that the formation took twenty minutes to form at most(!).