That is so, but it's so much easier with the luxury of hindsight. JB had time, but didn't know how much.
He would have known what time the farm workers would report to duty. He would be there.
The statement of Alan Fraser bell says that the workers would take direction off Nevill or Jeremy every morning on what their duties for the day was. That Wednesday morning to all extent and purposes would have just been a normal day at the farm.
If the workers could not get in touch with Nevill. They'd phone Bamber up. Don't believe they'd try kicking the door in. At the stage they'd be none the wiser of events. The first port of call would be Bamber to see what was going off.That would anyway only take place if they arrived at the farm before Bamber did. ( In the event he did not ring police)
With this in mind he would know he would have had ample time to watch Shelia demise after one shot and then go home and set the stage in motion. As we both said, it must have been a knee jerk reaction to shoot twice. A bad mistake in my eyes