Espresso, pour starts dripping halfway? I have a Espresso machine (Rocket R58).

I'm curious why my pour starts to drip halfway the pull. Is there any explanation why halfway and not from the get-go? 

I do understand I need to go more coarse to fix this...
There may be some advice on this. My first will be to check the pressure as you can do this with your pretty machine. Please check if you are around 9 bars when pulling the shot.

One reason of delay is, it takes a while for the water to wet the grounds. So, it is normal to wait for a few seconds to see the first drops. However; if it is more than a few seconds, the most possible problems I can think of are:


The pressure is not enough
You have tamped so forcefully
The grind is too fine