sql server – Should the T and L phase of a well tuned ETL report process take the same amount of time regardless of data size?

I have two different production systems where the total time for an ETL (Extract, Transform, Load) reporting process takes around 47 to 60 minutes whether the extract phase pulls data for 15 minutes, 1 hour, 12 hours or 24 hours. Yes there are vastly different amounts of rows for those ranges.

Is this normal?

I had expected that the total time for ETL when there is NO data would be …. well… a small amount of total time. But I must confess that I know nothing about the internals of the T and L phases within a report server.

Can someone shed light on whether the T and L phase’s are typically fixed in duration (up to a point)? I suspect that this process has not been examined or tuned.