I agree with all said.

I used to have to travel the M25 everyday for 5 years and the time you are talking about is not a good idea.

In the end, I avoided the M25 like the plague and did the A roads. I still left early enough to miss that time of the day. Like the others, I used to get near my destination and have breakfast and then on to work hey ho.

Deffo, book a hotel for the night before, or book a flight into heathrow.

Hope you get sorted.