My favorite moment in About Time is when Bill Nighy, playing a retired professor who can reverse time and relive portions of his own life, admits how he’s used this miraculous talent: to read thousands upon thousands of books. He’s like a superhero who flies around the world just to see cool stuff.

Using superhuman power to fulfill human-size desires is a great comic conceit. But the marketing of About Time presents it as something rather more cloying: a relentlessly adorable romantic comedy in which Nighy’s son (Domhnall Gleeson), who has inherited his physics-defying ability, uses it to woo Rachel McAdams. Judging by The Time Traveler’s Wife (2009), that’s just what time travelers do.

Writer-director Richard Curtis — who directed Love Actually and scripted Four Weddings and a Funeral — gives us a film with a broader scope than the ads suggest, relegating the romance to a modest slice of running time. At its best, About Time evokes one of the best time-wankery comedies ever made: Groundhog Day. At its worst, it gets scattered and pastel.

Gleeson’s Tim is a charmingly awkward carrothead whose family, living on the Cornwall coast, has quirk to spare: They’re like a cross between the Weasleys and the Tenenbaums. When Dad tells Tim about the time-travel gene, which manifests only in men of the family, the latter seizes on the opportunity to improve his nonexistent love life via multiple do-overs. It works, but only after many reasonably amusing scenes of trial and error.

The script presents McAdams’ character as a person with her own quirks rather than a prize to be won, and her romance with Tim as a realistic long-term partnership rather than a stroll into the sunset. Those are refreshing traits for a romantic comedy, but the problem is that About Time covers nearly a decade in episodic fashion, making it hard to focus on anything in particular. Curtis keeps introducing juicy comic or dramatic situations and then skipping ahead so we don’t see them pan out. Devilishly fun characters, such as Tom Hollander as a vain playwright, are wasted.

Perhaps this fragmented storytelling technique is intended to show us life from a time traveler’s perspective: Nothing has to be dwelled on, because everything can be revisited and revised (within limits, we eventually learn). In practice, however, the lack of focus leads to short-changing important milestones and superficial treatment of many characters and themes. Some of the setpieces feel dated and cheesy, and a subplot involving Tim’s troubled sister (Lydia Wilson) finds a far too easy resolution.

A movie that makes Big Statements about living every moment to the fullest needs to earn them by making those moments feel real and lived in, rather than bundling them into water-colored montages. Groundhog Day showed how a sense of grinding repetition (which is how many of us experience time) can give way to transformative appreciation. About Time too often fails to make the most of its fleeting moments, with a notable exception: the scenes between Nighy and Gleeson, whose father-son bond is by far the most compelling relationship in the movie.

Actually, just hearing Nighy explain time travel (it involves a “rumble and a stumble and a tumble,” he proclaims with Shakespearean diction) is pretty compelling, as is watching him play table tennis. Like reading thousands of books, little of what his character does is important, and all of it is great fun. High concepts may fall flat, but a brilliant performance is always worth your time.