How early is too early for check-in?

Basically, I have an upcoming itin. BOS-MAD-JNB (all on IB metal -- the "Other European Airline" forum is not that active, and since IB is a oneworld member, I figured this forum is my best bet for an informed response). The itin. was booked as a multi-city ticket.

The stop in MAD is a 2 day layover. I'd rather not have to carry my golf clubs and summer clothes to/from airport/hotel in MAD. Can I check them straight thru in Boston? What about checking them in upon arrival in MAD? If so, I realize the risks associated with such a move -- the clubs may never show up in JNB!! But I'd love to hear what others have to say on this.

Any thoughts would be greatly appreciated.

Cheers.