If its time related then start investigating power related things. The PSU would be the first thing to look at. Try powering only the bad blade pair (as long as they're the ones that power the controller) only and see if they still drop out. Alternatively, you could just swap your PSUs over and see if the problem moves.
Sometimes it happens after five minutes, sometimes it is overnight, sometimes on boot. I'll give swapping the power supplies a try next...
Swapping the power supplies had no effect. I guess I'll see what Bitmain has to say (they got back to me pretty quickly and asked for screenshots, etc), which I've just sent them.
They replied:
Hi,
Please go to "Miner configuration-->Advanced settings" and increase the voltage to a higher value to try.
Would have been helpful to give me a suggestion... there doesn't seem to be much if any documentation on voltage/frequency settings and I already set it to 0760. Any ideas?
That being said, I haven't had to restart it since yesterday morning.
The default with the first firmware for the C1 was 0725, the new firmware ups that to 0760. On the S3+, the default is 0770 and the new suggested temp. fix for the newest firmware is 0725. If you're trying frequencies then you might want to start in this range, but probably don't want to go too far out of those bounds (around 0800 would probably be highest for OC, unless others have tested higher, but you're voiding the warranty going above the 0770 -someone else stated 0772 but that's not what I saw with putty- would be my guess).