Oh, what fond elementary-school-age memories I have of The Time Tunnel! It's the first show I remember being canceled while I was actively involved in following it religiously. And it got canceled fast. Sigh. But this Classic Science Fiction blog (home of links to all kinds of wonders available online) points me to Hulu, where all 30 Time Tunnel episodes can be viewed online. Rendezvous With Yesterday is here:
It stars James Darren (who has a Star Trek connection), Robert Colbert, Whit Bissell (who also has a Star Trek connection), John Zaremba and Lee Meriwether (who is in the original series Star Trek). Irwin Allen is the creator of the series.
There's a Facebook group here. Fancast also has these episodes available online, but they seem to be hosting the Hulu videos.