Research on joint attention has demonstrated that individuals are sensitive to a coactor’s attentional relation to jointly attended stimuli. Within a chronobiological approach, a study was conducted to assess whether the presence of joint attention, as measured by the joint Navon effect, was influenced by the synchrony effect. Pairs of participants sitting next to each other were required to respond to the identity letters in a go/no-go Navon task. The joint Navon task was performed by morning, intermediate and evening types (81 pairs) at different times of day (09:00–10:00; 13:00–14:00; 17:00–18:00). The joint Navon effect on task performance was highlighted at the optimal time of day (in the morning for morning types, in the early afternoon for intermediate types and in the evening for evening types), but it disappeared or decreased at the non-optimal time of day, with the exception of evening types. The results demonstrated that joint attention was affected by the synchrony effect.