Hi Lloyd
The 30 second check in is a bit misleading. it used to work that way but these days the connections are more or less permanent. If you think about controlling a machine, often connections are instant, if the machines only checked in every 30 seconds you'd have to wait at times.
On the subject of the slow reconnects, we have quite a few more servers checking in so downtime is always out of hours and because of the number of machines we have it's hard to tell if we get a similar problem. I suspect not as the offline machines would show on our dashboards after being offline for 10 minutes. I've seen issues when our server has had a hiccup and all machines go offline and it takes a few minutes to recover but I put this down to 15k machines all checking back in at the same time and try to run procedures and upload logs all at the same time.
Have you looked at the Agent Log under Agent > Agent Logs for any clues as to why your issue might be happening? This is where I would start.