Under the One Electron Theory, positrons are created some time in the future when an electron decays, and destroyed at some point in the past when the positron

Under the One Electron Theory, positrons are created some time in the future when an electron decays, and destroyed at some point in the past when the positron decays back into an electron. So the lifetime of a positron is bounded on both ends, and never crosses the "big bang" singularity. It's not that antimatter 'created' in the big bang is traveling back in time, and only exists 'before' the big bang. It's that the big bang is when the antimatter is 'destroyed', turning into matter in the process.