Here is a SEDE query that counts the number of distinct users who have posted, and the number of posts posted, during each hour of the day on Friday and Saturday GMT.
On the X axis:
- 0 = 00:00 GMT Friday, or 7pm EST / 8pm EDT Thursday
- 12 = 12:00 GMT Friday, or 7am EST / 8am EST Friday
- 24 = 00:00 GMT Saturday, or 7pm EST / 8pm EDT Friday
- 36 = 12:00 GMT Saturday, or 7am EST / 8am EST Saturday
- 48 = 00:00 GMT Sunday, or 7pm EST / 8pm EDT Saturday
The graph shows that 10am BST (09:00 GMT / 5am EDT) is toward the end of a ~4-hour period of US-Eastern night that typically sees low posting activity, with activity ramping up for the next ~4 hours after that and staying high for the next ~7 hours.
It also shows that posting activity is typically very low over Shabbat. For a more seasonal look at how long the site's Shabbat lasts, see the same graph, for the past 90 days.
Here's another, more general query that shows every hour of the week. In this graph, 0 and 168 on the x-axis are 00:00 GMT Sunday, 24 is 00:00 GMT Monday, and so on.