One can safely portal back as far as about 1630 CE. Earlier is risky. I went back to July 862 BCE Manhattan. Wilderness, and rather cool even though summer. The long jump froze my unit. There four days subjective time as it rebooted.
No native folks I could find.
Though they found me, and were watching. I awoke on the second day to dried fish, and nuts wrapped in leaves next to me. I spent four days living, and being fed, and protected by the Mannahatta people.
I never saw the kind folks that took care of me.