Being serious I wouldnt even attempt to polish a red car in strong sun light never mind going over it with G3, your best bet would be to get it inside (if you can) so it could cool down and be out of direct sun light. When I did mine I started quite late at night (about 7.30 - 8.00 ish) and then started again the next day at about 6.30 am and I did a panel at a time starting with the roof.
P.S. It is good stuff but I think its fair to say that the best results would be to get it done with a mop and by someone who knows what they are doing, although I'm happy with the results I got doing mine by hand.