To me, lime juice seems to get funky more quickly than lemon juice does, lemon juice seems to be similar, grapefruit juice hasn't a rumor about it, and orange juice is picky picky picky. Jeffrey Morgenthaler has written in the Bar Book about the flavor preferences of Americans vs. Europeans and the volumes gained from different ideologies of juicing (refrigerated or not, and rolled or not), but I hadn't found any research into how two prolong these usable juice times, nor what physical evidence of degradation was occurring.
For each of the below citrus fruits, I compared varying time frames of vacuum sealed juices against varying time frames of fresh squeezed juices, in an attempt to find a ph-level correlation and a taste correlation. When is something no longer what we want it to be, and how long can we prolong that time frame?
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seriously, click images for results