I managed to complete this today in 25 degree heat after a pure disaster yesterday but it was a real mental battle. I had tried a new route yesterday as scheduled but I found it very tough as it had long slow climbs which caught me out as well as I messing up on pace badly. I was really annoyed and disappointed so I couldn't wait out the rest day and went at it again today on my local pitch. But boy did I have to push myself many times in the heat as I kept thinking of yesterday's failure and found my mind constantly telling me to stop and rest. I remembered something that I read on the forum that said just block out everything apart from counting one foot after another until you get past the mental block. It worked although I did have to slow down my pace near the end to ensure/drag myself through it. I'm tired after it but mentally feel back on track. But when that mental wall comes at you just push on one foot after the other!