When multiple shifts are defined on the same day and the hours you specify overlap, they are combined into one shift and are enclosed in one set of shift-indicator lines in the heatmap view.
For example, assume the first shift starts at 6 AM and lasts for 8 hours and the second shift starts at 1 PM and lasts for 8 hours. After you save these settings, the work-week lines and shift-indicator lines show a single shift from 6 AM to 9 PM. The Settings view displays the Total number of shifts per week reduced by one, and the Shift Duration indicates a longer single shift.