> Although, I think I do understand the meaning of it
>
>> In one hour before 8:30 am, when the reservations started
No, this sentence means "By 8:30 AM, which is an hour before the registration started, ...".
The actual registration starts at 9:30, which is written at the end of the article.
Here, is used as the apposition marker.
> * my friend Tanaka
> (compare: a friend of Tanaka)
> * Tokyo, the capital of Japan
> (The first is like "of", the second is for apposition)
> * 21 At the starting time, (which is) 21:00
>
As you said, 81 would mean "An hour before 8:30 AM" (ie. 7:30 AM).