Each job is a dependency for the next job. A long build time either indicates that individual assembly technicians have too many steps in their job (it is much harder to remember 25 steps than 5 steps) or that the plant is assembling more parts locally than their competitors. If you have an engine shipped in complete from your supplier that is less time your plant spends assembling a dependency at build time.
Electric cars should in theory assemble much faster than gas. Fewer parts. Less complexity in the mechanical assembly of the drive train.
When corporate overlords dictate that an assembly plant meet production numbers that it isn’t capable of accurately producing they shell out complete garbage. Inspection lines flag errors that managers ship with disregard in order to meet numbers. Every time.