Hello Tay Le
I would recommend analyzing the opens and clicks you have received on your previous Email Sends to see if you notice any trend in what times more opens and clicks seem to be recorded, and use that to determine at what time sending your emails produces the best results.
Some previously conducted research suggested that response rates for emails are generally higher at times outside of work hours, such as late night and weekends, so if this does not conflict with your findings when you analyze your own data, you could try scheduling some emails to go out during those times.