In your video it seems that the variables are applied AFTER the blueprint was placed and the robots already half or fully replaced the blueprinted buildings with actual buildings.

The variables should be applied FIRST and THEN the blueprint should be placed. Otherwise first wrong trains will arrive until you have finished your variable adjustments. Correct?

Yes and no.

The blueprint ghost and built entities will both have variables in them until you click "Apply". At that point, all variables update instantly.

Unless you incorrectly configure train schedules with variables in them, then you wouldn't have to worry about trains. However, it could affect the "cold start" of some circuitry.

Ah ok. So only variables are placed in the beginning. Thus no wrong values. Only placeholders. This is totally fine :-)