When is the right time to mediate — early, or after discovery is complete?

It depends on what's driving the dispute. When the fight is really about the number, mediating after enough discovery — key depositions, medical and damages records, the important expert opinions — tends to settle, because both sides can finally value the case on facts instead of assumptions. When the dispute is about something non-economic, or when litigation costs and relationships are themselves the problem, earlier mediation can save both sides substantial money and time before positions harden. There's rarely harm in mediating 'too early' as long as the parties have the information they need to make a real decision; the mistake is usually waiting until the courthouse steps, when fees are spent and everyone is dug in. I'd rather talk with counsel about timing than apply a rigid rule.