They were all dead by the time of Jeremy's second telephone call to Julie. The timing of that telephone call is irrelevant unless he was stupid enough to telephone Julie at Goldhanger before he purportedly knew that there was "something wrong at the Farm". All Jeremy needed to do was to make a telephone call from the kitchen at the Farm to his answerphone at Goldhanger,cycle back(which took DI Wilkinson 6 minutes) and replace the tape with a new one.
This has been discussed so many times..
Mr Arlidge,QC,,invented the bicycle theory,,like he must have invented a few things in his personal life too.! That bit of made-up fantasy was fed to the court/jury who then all went on to believe every other word that was said in that courtroom by him,,,and unfortunately not challenged,except by two of the jury,don't forget,,so Jeremy only " lost out " by a whisker.