Cramming does work, for a narrow purpose
Concentrating study into one long session before an exam raises performance on that exam, and pretending otherwise is dishonest to anyone reading this at midnight. Massed practice puts material into a state where it can be recalled shortly afterwards, which is exactly what a test the next morning requires. What it does not do is hold. Research on distributed practice consistently finds that massed study decays quickly, so material crammed for a Tuesday test is substantially gone by the time a cumulative final asks for it again. Cramming is therefore a legitimate tool with a known expiry date rather than a failure of character. The mistake is not reaching for it under time pressure; the mistake is reaching for it when there was time for something better.
What spacing actually changes
Spaced repetition takes the same number of hours and separates them with gaps, which makes each session harder and each retrieval more durable. The difficulty is the mechanism rather than a side effect: recalling something you have partly forgotten strengthens it far more than recalling something still fresh. This is why spacing feels less productive while you are doing it. A session where recall is effortless produces a comfortable sense of mastery and very little learning, while a session where you struggle to retrieve half the material produces the opposite of both. Students consistently rate massed study as more effective than spaced study and consistently perform worse under it, which is among the more reliable findings in the area and the reason the intuition cannot be trusted here.
Which to use, given the time you actually have
Count the days before deciding. Under about forty-eight hours, spacing has nowhere to go, and concentrated work on the heaviest-weighted material is the correct response to the situation you are in rather than a compromise. With a week, two or three passes separated by a day each will beat one long session built from the same hours. With a month, a schedule of expanding gaps is worth building properly, because that is the range where the difference becomes large rather than marginal. One thing is worth doing at every timescale: retrieving rather than rereading. Closing the book and attempting to produce the answer beats highlighting under any deadline, including the twelve-hour one. If a cumulative final is coming later, book a spaced pass for it now.