Except that by walking out, they're expressly turning their backs on the resolution...and letting everyone know where they stand.

Of course. The benefit of them having time before having to take a vote isn't that they'll be able to avoid any political blowback. If they're going to disagree with the resolution, they're going to do that. It's that they have enough time to "read the room" and avoid making any further missteps, like various pro-Palestinian groups did over the last week. None of them made speeches - so there was no opportunity to really screw up.

Rashida Tlaib and Cori Bush will have had two weeks to fine-tune their objection speeches to avoid pitfalls that a rushed speech on Monday morning might have included. Two weeks for them to see what reactions have been, to hear from their colleagues, to work their constituents so that those voters back home know (and understand) that the Representatives can't deliver a stemwinder defense of Palestinian rights in this environment. It's political malpractice of the gravest order to give progressives that amount of time to avoid the pitfalls and ill-chosen phrasing that a quick response might have yielded.