Currently the sales are at:
SSBB: 6.2M
MKWii: 6.3M
Wii Fit: 5.7M
SMG: 6.7M
SMG is averaging roughly 35K/week, so expect it to be at 6.8M in 30 days.
This means that SSBB will have to average roughly 150K/week. I don't think it will, as the Others initial boost is wearing off.
MKWii needs 550K, and a little less than 150K/Week. It will probably not make that, as it sells ~ 110K/Week
Wii Fit needs 250K/week, something which is unlikely.
I expect SSBB to pass it in 5 weeks, MKWii to pass it in 5 weeks, and Wii Fit to pass it in 5 weeks.
If you include this weeks numbers (19th), which I haven't, 4 weeks, so a month seems correct.