Establish top conversion time of day using analytics
Go into your analytics programme. Go into goals or eCommerce if you have an eCommerce website. Select total conversions and graph by day. Find the day with the highest number of conversions.
Now go into Graph by hour and establish the time of day that has the highest number of conversions. Do the same for conversion rates. Now you know what time(s) people are most likely to buy from your site. It’s worth experiementing to see if you get more success from an email sent at your highest conversion rate time of day or time of day with the highest number of conversions. These two figures will usually correlate anyway.
You should test sending your email at your peak time of week as it is is likely that your customers are most likely to buy your products at this time. However this might not correllate with the time of day and week that your customers are most likely to open an email. So you will need to experiment with this to achieve the best of both worlds.