Well the delay could be as innocent as they say. Just an unfortunate set of logistics. Most of the time these things take 2-3 days at least to do but that is in the off-season. No one cares or even notices. Now, because Spring Training has already started, people get all nervous because he is not on the field immediately after the signing.
Or it could be because they found something undesirable in his blood and they are contemplating what they should do next.
I kind of like the soap opera qualities of this whole JD affair. It's so Red Sox and so Boston media.