Unfortunately The Time Travelers is one of the weakest episodes of the new seasons. The movie itself is silly but not the worst movie ever made, which could be one reason for the episode not being that great in terms of riffing. On the other hand, the movie itself is not painful to watch, and it is pleasant to look at in as much as everything is clean and nice and the film quality is good so at least there's that (plus, Asa Buchanan).
The main reason I am giving this episode a 6/10 is simply because it contains WAY too many riffs. It is a non-stop onslaught which becomes exhausting and to make matters worse the riffs simply are not very good. There are a few gems tucked in here for sure, however, they become lost and not worth the annoying aspect of sitting through the rest of the episode. This is one of the prime examples of the crew not always understanding that quantity is never more important than quality. I think this movie would have been more well-suited to the crew in the first or second season of the original run when they did not feel the need to fill every moment with riffs, despite the riff quality, and actually sort of watched the movie.
Bottom line: this is not a must-see for fans (or for anyone else), I would not use this as a way to introduce anyone new to the show and if you are starting out in an MST3K adventure on your own, I would NOT start here. Save this for when you are running out of episodes. :P