I'd use two columns: one for the start date and another for the end date. Not only will this make the coloring much easier (it can be fully automatic), but it'll give you a better idea of how long jobs take.
In the screenshot below, I have created three conditional formatting rules.

The rules are all of type 'Use a formula to determine which cells to format'.
The rule created first (listed at the bottom in the screenshot below) uses formula =$B2<>"" and red as fill color.
The rule created second (listed in the middle) uses formula =$B2>=TODAY()-14 and yellow as fill color.
The rule created last (listed at the top) uses formula =$C2<>"" and green as fill color.
