> The fastest we can get to around Martian orbit is 7 months.

This is not accurate. Viking got there in <4 months, and we have the technology to do it even faster, if needed. The long duration transits are often the least energy (Hohmann transfer) and that's why we use them. Planetary alignment is also a big factor.

Anyway, there are currently proposals to have probes lingering in high orbits and intercept interstellar visitors (maybe not as fast as 3I), and Rubin should give us plenty of targets when it gets online.

As an interesting tidbit, 3I was found in the Rubin data ~2weeks before it was spotted. Should be a perfect exercise in refining the discovery algorithms.

Viking probes got there in about 11 months. You might be thrown off by an AI artifact.