I have a similar situation - and gave myself a Sunday arrival from SFO and Monday departure to MAD and onward to IST. There is no way I want to lose a day at IST on an award, or even less, miss my Marmara Sea / Greek Islands cruise.

ORD can be a mess - I have been involuntarily rerouted several times connecting in ORD, but always on through PNRs. With separate PNRs, you are late due to an AA flight delayed arrival as you are if you forget or get caught in traffic; IB really has obligation to you (see hillrider below), but it's difficult to say what they would do; some of us have reported less than stellar IB customer service at times, particularly on the ground - and they have but one daily flight, so it could be consuming of your BCN time, to say the least.

You don't mention when you are attempting this, but winters, ORD has delays due to nasty weather; summers, ORD has delays due to nasty weather; in between, they merely have nasty delays. Not to mention, depending on your travel, the BA and possible AA strikes might affect your travel plans as well.

Personally, I'd see about changing my flights to arrive earlier in ORD, or at least doing a confirmed same day travel change and arriving at ORD earlier - much cheaper than change fees. YMMV, of course.