[yrb]

I would say the biggest factor is that it is a very repetitive rectangular box.

Overall design and how it is detailed is the dominant factor in time it takes to build things.

Do I have lots of joints that have to be perfect or can they be rough cut and covered with trim?

Do things assembly easily without having to fiddle due to having the correct tolerances?

Cuts and joins are what take the most time. The less cuts and joins you have the cheaper and faster things will be. Also cuts and joins that have to be done to high tolerances take a lot longer.