Change Start dates upon duration days change in Project timeline calculation.

All,
Need your expertise once again!!!
I have a worksheet with three separate sections: Current, Amended and Final.
These represent a continuous improvement project I am investigating for my firm.
In the attached dummy file, columns A, I and Q show will show the step processes to develop a widget and the number of steps will continuously alter,
Each process step has a start date and an estimated duration. (Columns B:C, K:L, and R:S respectively). The estimated Final date is calculated by formula in the similar labelled columns.
As I have quite a few worksheet changes, what I really want are macro’s to auto-increment and override the existing worksheet changes IF the associated button in columns i:k are pressed….to produce a continuous range where each start day is the same as the previous processes steps finish date.
In other words, if I change any duration time (for example) c22 to 33 days duration, then the remainder of column B will adjust incrementally.
I cannot seem to get this right, so seek your help!!
Thanks for looking.

Skyping. Please see dummy file for perhaps a clearer explanation!!

I seem to have found a method (its slow, BUT WORKS!!!)

See below.....any advice to try and speed it up would be greatly appreciated!!!

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