Yes, sooner is better. Mine's on Tuesday. I'm enjoying being on this high so much I hope I don't chicken out for fear of being given a sedative. I'm trying so hard to be good and "behave", but it's really hard when I'm like this. I feel like my veins are filled with caffeine, adrenaline, and sugar. Can't stop fidgeting.
If I've not said so elsewhere, bring your journals, a list of symptoms, anything that will help you in case you're not sure what to say or go blank in the interview. I often take my medical info, blood tests, mood charts, journal, etc. into a new drs office even if I never take them out. They're just for reference in case I'm asked a question I don't recall the answer to. Like, "How long have you been feeling this way?" For me, an hour is like a day, a day like a week, a couple of months more like 6-12 when I'm depressed; but it's just the opposite when I'm hypomanic, so my sense of time is like, what day is it? 3 weeks have passed? No, that's was just yesterday, right? It's dark outside?
Anyway, that's just an example. Bring whatever you have even if you never use it. It may be helpful if you get stuck. Best of luck.