Note that this "strength was greatest at noon" was also said to be true about Gawaine, and there is a version of a combat where after the noon hour his strength waxed and he was defeated.
"According to the Vulgate Mort Artu, Gawain had been baptised as an infant by a miracle-working holy man, also named Gawain, who named the boy after himself, and the following day announced that every day at noon, at the hour of the baptism, his power and strength will increase."