Complex sentence: If they had been working correctly then Tinsley would taken over from Meakin at 6.00 am, however the two men had an developed an informal arrangement allowing whichever was working the early shift to arrive later.
Split into simpler sentences: If they had been working correctly then Tinsley would taken over from Meakin at 6.00 am. However the two men had an developed an informal arrangement allowing whichever was working the early shift to arrive later.