The protagonists sometimes notice that time has passed by looking at objects outside the ship, as they don't perceive the activation and deactivation of the stasis field otherwise.
People without hypersensitivity may be able to perceive some of these things, but generally don't notice them, whereas the hypersensitive have great difficulty ignoring them, or are unable to ignore them.
His entire family has a gene that allows them to subtly perceive other people's twitches and nervousness, and the tight bracelet allows Apollo to notice more easily when he's subconsciously perceiving it through body temperature increases and the like.