Ecommerce conversion rates by time and day and day of the week.
Activity on your site depends on the industry vertical you are in. Products which need a family decision (like furniture) may be bought on the weekend, whereas work-related products will see weekday purchasing. Impulse buys will be more evenly distributed across the days.
This report looks at the last 90 days of purchasing. Independent of any particular campaign, there is likely to be a weekly pattern for the average user.
You should focus your marketing activity on the periods where users are already buying, so each 'click' you acquire has the highest change of leading to a sale.