I can't say for sure but what we do is use the actual users timezone to deliver it at the right time for them. This does of course take some A/B testing and depends on what action you want the users to take!
These days the ESPs are using their data and customer email sending patterns to come up with a feature that allows software to choose what's ideal time to send an email to a person based on various factors. It does work most of the times. SendInBlue has it, I guess Mail chimp too
@repreneur If you are purely into Outbound email reachout, those 2 wouldn't be much ideal...They also have strict regulation in place on how you collect the emails and the quality of emails. Spam & bounce rates are constantly monitored for each campaign.. They want to make sure their entire customer base gets benefited out of healthy email sending habits.