Hahaaa...!
I don't remember exactly how far in advance it was, but, I think it opened up about 6 mo. in advance, kinda' like ADRs.
All I know is that it was on a weekday, 'cause I was here at the office, and 5 of us were on different computers at the same time trying to make sure we all got registered before all the slots were taken.
And, no, you definitely don't have to be a serious runner, but, you do need to keep at least a 16 min. mile pace, or they'll pick you up off the course and take you to the finish line. Hopefully, my feet stay fine, and I'm not one of those lucky ones in a coupla' weeks...

We're all really looking forward to it...!
BTW, good luck with your DH...!