There's some real signal here, though it's more about avoiding bad times than hitting one magic perfect time. Tuesday through Thursday, mid-morning (around 9–11am) in the recipient's timezone tends to perform reasonably well across a lot of B2B audiences, since it's after the early-morning inbox triage but before lunch. Monday mornings and Friday afternoons tend to underperform (inbox is either flooded or people have mentally checked out). That said, your specific audience matters more than general rules — if you have enough send volume, testing a few different windows against your own list's actual open rates will tell you more than generic guidance will.