I enjoyed creating that and am pleased it works.

If you have problems with the rest of it let us know.

I would simply put the dates for all the columns except the first shaded one
as x plus 7. (i.e. the formula in E1 would be "=D1+7" copy this formula to
all the relevant cells to the right.and format the cells as dates) then you
only need to put the first date in D1. I would do this manually.

The single line idea is feasible but I think it would be a pain to track back.
One option would be to change the present  macro to add a number  1 to 6 (for
the respective stages) each cell  as you colour it - you could set the font
colour the same as the interior colour so the numbers are not visible. Then
use the countif function to put a row  of counts (I would put them at the top
rather than the bottom) for each stage. The higher numbers would show  the
higher concentrations. You could colour these as well but the code  to do that
would need to be at the end of the macro as it would be working off data
changed by the earlier part of the macro.