Window Cleaning Schedule

Building A

Can't happen first

Building B

Must happen before Building D

Building C

Must include the $12$th in the schedule

Building D

Must happen before Building A

Question

Four buildings are scheduled for window cleaning, one at a time. Each building takes $4$ days. The cleaners do not start a new job on Mondays or work weekends. On which date should the work on Building A begin, to complete all $4$ buildings as early as possible?

Calendar

$\backslash$table$[[$SUN$,$MON,TUE,WED,THU,FRI,SAT$],[7,1,2,3,4,5,6],[14,8,9,10,11,12,13],[21,15,16,17,18,19,20],[28,29,23,24,25,26,27]]$