What Model or Calculator should I use to set the right target?

#1
I have a production target in which 90% of widgets must be completed within 2 hours.
The production process has two main components. Process A + Process B (together these have to be completed within 2 hours, 90% of the time).

(quick note: Process A is the simpler process)

I want to establish an accurate target for Process A and for Process B independently that will add up to 90% for the total outcome.

I tentatively set the targets as follows: Process A target = 80% completed in 30 minutes; Process B target = 80% completed in 90 minutes.

Total daily widget count average is ~ 400 units

What is the best way to look at this?