It may have been sufficient time if it were a pre-meditated attack (which the prosecution do not claim it to be). Then the attack and 'escape' plan would have been worked out in advance. But this was considered to be entirely due to a momentary burst of anger. He would have had to go from at worst bit flustered when returning from do-it-all. In particular the other girls do not report him getting angry when with them either before or after this window of opportunity when the attack was said to have taken place. Then bursting into a rage when seeing Billie-Jo, attacking her with the spike, to calming himself down and cleaning up any blood and sweat from his face and hands. Then finally coming up with a plan of what to do. I'm sorry but the window of opportunity for all that is at best tight or simply not feasible. Why do you think he wouldn't have had to clean up? There was blood on the spike so it would have been on his hands.
The prosecution's case was that he flew into a fit of rage due to frustration from the wasted journeys to both the supermarket and do-it-all, then to be finally confronted by Billie-Jo making a mess of painting the window frames. Again this stretches credibility as this rage would have been without precedent. He had raised the other other girls and was an experienced teacher without any angry outbursts of note. The family were under the watchful eye of the social services due to fostering Billie-Jo and applying to adopt her. Nothing had ever been reported and none of Lois' subsequent claims were corroborated by anyone else. Including their live in nannies.
Finally, it must be remembered that the reason the patio doors were being painted was after them being repaired due to the latest of a series of attempted break ins.
Please air your views on the matter, I would like to hear them.