I don't think they're too many free programs to do that... I used Luxion Keyshot 2 for these renders
Rendering time? About 7 minutes each one, at 1800x1050
"It's not free", but I think the trial allows you one month. I also was part of the beta tester members for Bunkspeed Shot, which has been released recently, I'll try the final version shortly

There are many others, aswell as plugins for your 3D software like 3DSMax, Rhinoceros, Maya... but none of the ones I know are
legally free...