This is a rather artificial scenario, but it has been bugging me lately.
Due to the confinement in QCD, quarks are bound in color-neutral configurations. Any attempt to separate a quark from this bound state costs so much energy that it's enough to pair-produce new quarks, hence the quark-jets in accelerator experiments.
I'm now considering the reversed (hypothetical) scenario. Assume the you initially have two quarks (up and anti-up for instance) that are placed far away from each other. Buy far I here mean further than any other length scale in CQD. Now, let the two quarks approach each other, as in a scattering experiment.
At what distance does the two quarks start to interact, and what happens? Since the strong force is confining, the interaction should be stronger the further away the quarks are, but they cannot interact outside of their causal cones, so how does this work at really long distances?
I'm imagining that the "free" quarks are in a metastable state and the true ground state is the one where several pairs of quarks have pair-produced to bind with the two initial quarks. Thus the closer the two initial quarks are, the smaller the energy barrier between the metastable and the true ground state becomes. Thus at some separation $r$ there is a characteristic time-scale before pair-production occurs.