Board Thread:Questions and Answers/@comment-33062853-20171016141954/@comment-16461120-20180219053623

This feat would require Barry to move at Mach 10,925,375,000,000,000,000+, which is far greater than Flash's erroneously previously stated "max" in this thread; meanwhile, Pietro's top speed is never actually specified that I can find, though as I previously said he was shown to have inexplicably been boosted to greater than Mach 874,030 during Assault on New Olympus.

Either way, Quicksilver still appears to be trillions of times slower than the Flash, but the question itself regarding his ability to time travel was answered in the affirmative during Son of M.