One who has davened in one minyan can certainly attend another minyan later on for the same service, and he forms that minyan. That's often done. Good. Now extend that concept. A person is davining yehidis (alone). He davins, goes back in time to the beginning of the davining, and davins again. And again goes back in time to the beginning of the davining, and again davins, etc, nine times. So we have the same person, appearing ten times in the same room. Does that count as a minyan and bring down the Schinah? Maybe not. What about the rule that 6 out of 10 must be "davining" and not just making the minyan. If he goes back in time, after davining once (say, for mincha) is he now re-required to davin the same Mincha? Or, perhaps, if he goes back in time before he davined Mincha, then did he davin yet? Who davins for the amud? What if he was a chiyuv? Who has Kadima (precedence)?