Need help on sampling

I am very new to statistics so forgive my ignorance...I just need some help to get pointed in the right direction.

I need to take some baseline time metrics (how long it takes to do Process X). I will then develop a workflow improvement process and then take an "after" time metrics. In theory, Process X will be completed in a much shorter timeframe.

Since this process is performed in many different departments, my thought would be to take a cluster sampling of each department. I could determine the confidence level and calculate the number of samples I would need to take.

I will repeat...I am VERY new to statistics so I would appreciate any direction at all.

Does this sound like a reasonable plan?

Thanks in advance...