Problems with send intervals

Let me start with this: If you experiment with daily intervals (turning daily on or off) then let at least two days pass before you start watching for a pattern. The behavior is complex and it may appear chaotic when you play with various intervals, but it's working correctly for thousands of D6 sites.

Please try to not do everything at once. Leave digests disabled until you've confirmed that the intervals work correctly. Then turn them on and keep them on until your tests are completed.

No email are sent if the interval is set to 1 second and digest is enabled.

I'm pretty sure those mails will arrive once your longest interval has expired. We have no confirmed reports of ever having lost mails due to intervals or digests not working correctly.

Please let us know how it goes in due time.

So, what did you find?

No follow-up.

Adding a question here as it seems the best place if you don't mind.
I have recently installed the subscription module - Drupal 7 version.

I have am testing two intervals: 3 hour and 1 day so have a test user account (for the 3 hour interval) and have set it to one day for my admin account.
So, I also checked digest and this is working fine. I get all new changes (which are related to new posts in the forum) all in one email for both accounts. The main issue I am having as when there has been a new comment or post in the forum, the messages are being sent out on the next cron run no matter when that is.
I have been testing this for about a week now, so have been periodically logging in and creating a new post or two and then not logging in again and just waiting. Sure enough when a message is sent, they are both sent at the same time and not at a particular time. If I log in twice or even three times in a day to make a new post, then at some point in the future (not a particular time after, just at the next cron run) I will get a notification email to both account emails at the same time, and if I log in again that same day and post again, then even the 'every one day' account will get another notification at the same time as the other, on the cron run and therefore not after a whole day has passed since the last email.

I hope that makes sense.
I have tried to set up a more consistent cron run by adding 'Ultimate Cron' and setting this to every 30 minutes, so I don't have to log in to initiate a run, but this isn't working as planned, but cron is still running more often than it was (the last time the notification was sent out about 2 hours and 40 minutes after the forum post was made.
Please note that no one else is logging in to the site so they cannot trigger anything.

So I wonder what I should be checking to see why the interval choices are being ignored.

Thank you.