Because I could not help myself, I did more mad math:
Each square takes the customer 1 second to walk
To register is 5 seconds
Eating takes 10 seconds

With an optimized 4 door layout it takes an average 5 steps post register.
With an optimized max (over 20) door layout it takes an average 3 steps post register.

4 doors customers spend 20 seconds in bakery
Max doors customers spend 18 seconds in bakery

Those 2 seconds of savings yields a 11.1% increase in revenue.

So I would not recommend exceeding more than 4 doors until you have enough ovens to keep red velvet cakes in stock (aka spend your diamonds on opening more slots for ovens).