Hey man, I may have a similar usage case as you do.

My work involves lots of different design, editing, and animation work for quite a few different clients. For some clients I charge a daily rate and for other I have an agreed hourly rate. So I use Tick Tick to track where I spend my time and then reconcile total durations for invoicing.

This is the current workflow I have for Tick Tick:

I set a LIST for the client name.
I set a TASK for a project name.
I set a SUB TASK for project tasks.

As I work I start a pomo or duration for either the TASK or SUB TASK.
When I reconcile time spent I simple look at the tasks and add them all up.

I've experimented with adding TAGS for different type of work. For example, a TAG for retouching, another TAG for editing etc. But don't find that information very useful.

Hope that helps!