This illustrates the fundamental problem with small-scale transatlantic ops. One roundtrip occupies an aircraft for a day, with absolutely no leeway if anything goes wrong. History is littered with failed airlines who never grasped this fact (although there was one notable exception - Virgin Atlantic).
EOS have realised that their reputation will not survive a rash of schedule disruptions and have taken the only precaution they can by providing a spare aircraft - one very expensive asset just sitting idle.
A quick calculation would give an annual utilisation figure of about 2800hr/aircraft - industry benchmark for long haul is about 5000.