de retard vs en retard

Question

In the Kwiz - Why is "J'ai dix minutes de retard” correct, and

“Je suis dix minutes en retard”
is not?I know it's simple, but I'm not seeing it.

Accepted Answer

Different word order required.  
Être - Subject/verb/late or early/time period
Avoir - Subject/verb/time period/late or early  
With être “ je suis en retard de (dix minutes)”. 
English allows changing the word order with ‘to be’ so that we can say “I am 10 minutes early/late” instead of “I am early/late by 10 minutes”. French insists on the latter phrasing with être.
If you think about it “I have 10 minutes” makes some sense but “I have early" doesn’t. On the other hand, “I am early” makes some sense, but “I am 10 minutes” doesn’t. That might help with remembering avoir/être. 
(Unfortunately it doesn’t work quite the same with arriver/venir/finir/commencer, but always the exceptions)!

Answer

Sometimes it helps me to get into the head of French people and "feel out" how they think about expressing something:

Je suis en retard de dix minutes. -- "I am in delay of 10 minutes."
J'ai dix minutes de retard. -- "I have 10 minutes of delay."