I can confirm that the scheduled actions definitely don’t always run on time. Sometimes up to 10 mins late. According to support this happens because the system

I can confirm that the scheduled actions definitely don’t always run on time. Sometimes up to 10 mins late. According to support this happens because the system gets overloaded sometimes. I had some content slip through into my main site a day early because the job that rebuilds the site at the end of the day was 10 mins late, and in the interim new content was added so when the job ran it got lumped in. I will probably have to re-architect the whole workflow at some point but it’s good enough for now.