Nancy,
Is it it the same for summaries?
No, Summaries are once per day regardless of the amount of traffic in the group. For GMF mine have been arriving around 6 am U.S. Pacific time. I don't know if that's true of all groups.
We are trying to determine if a Digest is generated after so many
(12 ?) messages are posted to our group. Or is it a 24 hour period?
Both.
To amplify on what J said, for Digests it is once per day, plus once per 12 messages if there are more than 12 in the day. For GMF my dailies have been arriving around 10:15 pm U.S. Pacific time.
Example: 18 messages posted will generate 2 digests a day.
Correct. A digest of 12 when twelve have accumulated, and a digest of 6 at the end of the "day".
NOTE:
Digests need not be the same for all members.
If a member has muted a topic or hashtag then his/her digest(s) will contain fewer messages. In your example, that member may reach a total of 12 later in the day than other members, or might not reach it at all and receive only one digest. Or even none if all of that day's messages were in topics or hashtags muted by that member.
Likewise, members using advanced subscription preferences to receive only messages they follow will have fewer messages than those members who receive all messages.
Shal
Shal Farley