"do I really care if it takes twenty minutes instead of twenty milliseconds?"

No, nobody sensible cares. But the stuff people are suspicious of is supposed to be regulated so that your executions are only improved. If somehow this isn't true, it should be a bright line crossed and a big scandal with people going to jail or at least big fines.

Then again, if you panic over a "flash crash", then I guess you should be concerned about liquidity?