While the typical answer is 33 beats per minute, musician Adam Neely's answer morphs into a great primer on the "perceptual present," a concept widely discussed in both the philosophy of music and of consciousness.
In The Principles of Psychology, philosopher William James considered the perception of time and concluded that we all live in the "sensible present," a period of time more like a segment on a line than a point:
In short, the practically cognized present is no knife-edge, but a saddle-back, with a certain breadth of its own on which we sit perched, and from which we look in two directions into time. The unit of composition of our perception of time is a duration, with a bow and a stern, as it were — a rearward — and a forward-looking end. It is only as parts of this duration-block that the relation of succession of one end to the other is perceived. We do not first feel one end and then feel the other after it, and from the perception of the succession infer an interval of time between, but we seem to feel the interval of time as a whole, with its two ends embedded in it. The experience is from the outset a synthetic datum, not a simple one; and to sensible perception its elements are inseparable, although attention looking back may easily decompose the experience, and distinguish its beginning from its end.
The perception of time has also been examined by music theorists. In The Psychology of Music, Diana Deutsch estimates the perceptual present lasts 3 to 8 seconds, ty[ping that estimate to the baounds by which music tempos feels like music.