The sending time for your emails can be set up in the workflow Settings tab > Email sending section.
You need to configure three parameters of the sending time:
Time Zone: the time zone of the workflow is set to the time zone of your profile by default. You can change it to the time zone of your prospects if needed.
Send emails on: select the days of the week when you want us to send out the emails.
Send emails between: set the "sending window". We'll send emails only between the selected hours.
Note: there is no way to select the exact time for the email to be sent out.
Please, note that the emails are sent according to your sending limit. It doesn't matter how big the sending window is, once the limit is reached, the system will stop sending emails for this day.