What Factors Impact Route Time Variation?

Hi All,

I'm looking for a resource to understand how routes are determined by SAP, what the system-generated dates are, what inputs impact route planning and date planning in the system (e.g. plant hours/days, customer receiving hours/days) and how they impact.

Basically, we have the problem that our routes which say 3 day are turning out to be 2 days or 5 days.  I want to work on standardizing, but don't know where to start.

Thanks!

-Max