Transit in Urumqi

Hi
I booked a flight from Dubai to Shanghai, and another 4 days later from Shanghai to Hong Kong, assuming this would qualify for a 144 hour transit visa.

However I just realised that the Dubai to Shanghai flight is via Urumqi, and it's an 8 hour layover...
Questions are;

A) is it possible to have such a long layover in Urumqi while heading for a transit visa destination? I saw somewhere that you can only wait up to 2 hours

B) if I change the flight so that the Urumqi connection is shorter than 2 hours (there's a flight to Shanghai 1:50 minutes after I land), where do I get the 144 hour free transit, since I'll be arriving in Shanghai on a domestic flight...
Many thanks for your help,
Lisa