Hypothetically speaking would a less than 10ms gap be acceptable? How about 5 or 6ms?
I think there are three basic camps here:
<1> Only truly seamless will suffice, won't consider any other option
<2> I don't care if it's seamless as long as I can't hear it
<3> Split schmit...I'll make the break at an opportune time during the performance
So I think what you're really getting at with your question is the <2> group, and to satisfy them the split needs to be inaudible. However many ms that is...well...I don't know. It may depend in part on the source material. Obviously, <1> is ideal.