Especially since this was not planned as a flyby from the start, it was a secondary mission.

I believe somebody has already landed on an asteroid, either taken samples or impacted something into it. So I don't think it is extremely difficult making the rendezvous and matching speeds. I just meant to point out that the dynamics don't always let you land somewhere just because you're able to get there. If you do rendezvous with another solar system object, and you plan to do it at a relative velocity slow enough to do something other than crash into it, it is probably at only one place and time. And it may be very far away and way in the future.

I say this because you often hear people say things like

"Asteroid X comes within a million miles of earth every year or so, we should be able to fly there, land, and tour the solar system aboard it, and then jump off and come home next time it approaches earth."

It doesn't work like that. When its near earth it may be moving so fast relative to us that matching speeds would be highly energy-expensive. On the other hand, a transfer orbit that meets it on the other side of the solar system a year or two later may be fairly cheap energy-wise. Of course, in order to come home, you may have to stay there a long time, and your trip home won't start when its near earth.

As I recall, the cheapest trip to Mars takes nine months, the trip back takes the same, and you have to stay there over a year for the alignment to be right to come home. You can do it in less time, but it will cost you.