BRAC Cycles and Work Rhythm: A Detailed Reading of the 450 Minutes in the 08.00-17.00 Office Day

This paper provides a detailed explanation of the 450 minutes used in the analysis of the standard office working day, 08.00-17.00. It shows how 450 minutes is derived from the total presence time of 540 minutes, after subtracting the 60-minute midday break and the 30-minute closing phase. The remaining 450 minutes are then divided into five Basic Rest-Activity Cycles (BRAC) of 90 minutes each. The paper clarifies that Cycle 3, which is interrupted in clock time by the midday break, remains continuous in effective working time, consisting of 60 minutes before the break (11.00-12.00) and 30 minutes after the break (13.00-13.30). A parabolic model is used as a semiotic bridge to interpret the peak of attention within a cycle, with the characteristic peak value of 506.25. The study treats the 08.00-17.00 office day as a shared cultural pattern and reads it through the BRAC framework.