It depends a bit where earth and jupiter are in their orbits relative to each other. These probes with their 680m km range were designed to cover the inner solar system up to and including Jupiter, but launches will need to be timed correctly due to the fact that earth orbits at about ~150m km and jupiter sits at ~780m km from the sun in this game. Meaning that if earth is on the other side of the sun the probes can't reach jupiter.
Still, that will only delay things by 6-9 months or so, if earth is only just leaving the good zone.
As for that building schedule - building a naval shipyard takes time and resources too, and retooling it to switch from the survey design to the (un)armed design, ditto.
Especially if you skip the 'engines' phase of that research and just have some people jump into civilian ships with conventional drives immediately
(Yes, those are *terribly* *terribly* slow ..)
Well, 6 months is a lot of time. And the first shipyard will take 600 BP only instead of 2400, i did so because this way everyone can build it without needing 1000 CI or more. So you see, i already made all the considerations, and in my case, as EU, GE ships are more convenient than probes. But nothing prevents me from using some, it's just a relatively low industrial and scientifical expense. And conventional drives are, uhm, like 30-50x slower than Thermo-Nuclear Engines. And these are not really fast, with 2000 Km/s on a small GE vessel. And 40 Km/s is a pain in the ass, believe me. I didn't even list that possibility, because it offers no practical advantage.
