I really liked the concept, but their complete lack of understanding time travel was beyond facepalm-worthy.
I was yelling at the screen.
First of all, when is the timeline actually updating for the people still in the present day, and why do they act like the timelines are running concurrently? Ok, the time machine takes more than 3 minutes to return after Flynn does, so let's hurry up and start digging up where they landed to find the capsule thingy. News flash - it happened hundreds of years ago, they're long dead, and there's no rush. Anything Flynn did in the past has already taken effect too, so if the timeline is screwed, the timeline is screwed. And shouldn't the time machine aim to return immediately after it left? Both time machines should be doing this, so there's no reason for a delay, except for again mistakenly treating the timelines as concurrent.
And they had to hurry up to catch and guide the time machine while it was in transit. The time machine actually departed hundreds of years ago, how are they acting like this is something currently in progress? THIS IS TIME TRAVEL 101, PEOPLE!
If you treat this as realtime as this show does, there actually should have been an iteration of the timeline where they failed to get back and died, because the timeline had to update first for your message to survive till the present day. It's like they used Bill and Ted's Excellent Adventure as their example of time travel mechanics.
The lesson is you just can't use causality when you treat time travel that way, it doesn't work.
And how did they perform that repair to the hull of the machine? It was this perfectly round patch that was secured with screws or something. Just how? It almost made the capacitor seem plausible (and here they put the obligatory flux capacitor reference, because time travel fiction will never live that down). Ignoring the unlikeliness of only requiring one capacitor to fix the circuits, and the ability to make a practically usable capacitor in those times, the charge it would hold and its reliability would be so worthless that they'd have probably been better off just bypassing it altogether.
As I've said, I do enjoy this show, but it is so damn stupid.