This is not normal. The problem is clearly getting worse. The engine should start in 1/2 second when warm, without any glow plugs and without your right foot on the pedal.

Have the basics of valve lash, cam timing, and injection timing been checked recently?

A properly running 617 with good compression can start in 1 second when cold (12 degree ambient) after a proper glow cycle.

This one has some serious issues that need attention.