At 8.30am every Sunday (3.30am Eastern time and 12.30am Pacific time), I receive a dozen digests from various community groups I’ve joined (all hosted on Salesforce platform).
I can’t think of a worse time to receive a digest.
This is the problem with using the default platform options. Often the platform provider gave as little thought to the default settings as you have. You need to go through every single setting and make decisions that reflect your strategy.
A digest is probably best sent out on a Monday morning, any lunchtime, or Friday afternoon.
Also, consider the member experience. If a member has joined a dozen groups within a single community, they’re going to get a dozen digests all sent at the same time. Either change the timings or switch the digests off for some groups.