Hello, not sure if this is a project management question more than a software question. It concerns deciding what % availability to use for my project resources.

I have an electronic task tracker with over 12 mths data detailing how people spend their time, split between ad hoc and project.

In my calculations I have subtracted the ad hoc from the total time worked rather than calculating what proportion of time people spend on their projects. My assumption is that project work is more inconsistent than ad hoc as we are a small company who need to be responsive to issues.

Can anyone spot any risks/flaws in my assumption?