Currently, I have it at 86400. But it says there that "The current value for this field is invalid. You must update it." What is the best / commonly used value for a second nameserver?
For most intents and purposes, the defaults (86400 or 1 day) should be sufficient. Just hit Save Changes and it should 'set' the default value as the default.
The problem is it said there that that value was too high. I currently set it to 10800 (3 hours) but was wondering if there's some other "magical" number that everyone uses.
Well, it is wrong. Not sure why it's telling you to use 10800, 86400 is perfectly fine. But glad you got it resolved.