As referenced in Hearing in Time (London), a timepoint is a specific moment in a temporal construction. According to Hasty and Schachter, timepoints may not have accents or emphasis, only events occurring at timepoints can (London, 2012: 21). They are durationless, and can only be specified relative to surrounding timepoints.
For example, “the downbeat of measure 4″ is a specific timepoint in a piece. It is not given a duration or note-value but referenced as an instantaneous marker in time.
London also remarks that “time points correspond to peaks in attentional energy and mark other phase relationships in the attentional cycle” (London, 2012: 22). Timepoints can thus be thought of in terms of their relationship with entrainment of rhythm in the brain.