Find equal or Next Date

Hi Guys,
I have a spread sheet that I use to manage some projects (Programme)
What I have is the project name's in B5, B6.....B117
In C5 I have a start Date of the project
D5 Calculates the if it is over or under time.
I only enter dates in the (red Accent 2 80%) what i call a pinkish colour.
Now it seems to work if the dates flow from one cell to the next.

What I need is to work out a way to allow any part of the project to be completed (Could be at the end or middle) and it not give error and work correctly.
I need it to basically look for dates entered and grab the date that is equal to the date entered in that row series or the next date down.
Can this be done?
Thanks in advance if you can help.

For example I will enter a start date in c5
Then I put a date in F5, as E5 and G5 are calculating based on them.
This part works. If I then enter a date in I5 this will still work as it is always looking at the previous cell refrence.
I need it to also work even if I didn't put a date in I5 but had to put a date in AA5,
so entering in the date is not sequential but can be spazmotic but all along the same row and be able to replicate the formula (or VBA) in the rows below.