Accumulating Time - Professional Services Firm

Good Day,
I am trying to create a model to represent time in a professional services firm. Time moves from work-in-progress (WIP) to a pre-bill and finally to a bill. I want to be able to review the age of the WIP. I am leaning towards the accumulating snapshot. I am envisioning 3 rows per time entry considering that time has 3 states with the relevant role playing dates. There is the other thought to have a more horizontal structure where I have a lag for each state. This is a hard concept for me to grasp. Thoughts anyone?

You only need one row with three dates. Add lag metrics as needed or calculate on the fly.

Sounds like a plan. Thanks