Zevahim 31: It's a Measure of Time: Half a Loaf of Bread

What happens if the olive's measure of the offering was eaten in combination by 2 people? Is the concern that an olive's measure is eaten, or that the given person ate the olive measure? Or what if the olive's measure was eaten over a long, slower period of time than the usual "half a loaf of bread" time frame? Plus, even if the olive's measure was divided or slow, etc., it would not invalidate the offering - because those same actions don't combine.