Miracle Time Possibly Rigged?

Carved Slot cubes do give a notice when you hit legendary though:

 Spoiler

http://new.tinygrab.com/a395c0272e91295d...48c139.png can't embed two images so here's the first

I feel more like it was working as intended until about 30 minutes in and then the rates plummeted for everything. Most people I've spoken to started off using bonus potential cubes and then moved on to regular potential (black cubes) afterwards.

I don't think the timing has anything you do with it. Since most people you talked to started out with bonus pot cubes and then used reg pot cubes afterwards, doesn't it make more sense to just say that the reg pot rank up rate for unique -> legendary is pretty low (as in lower than Super cube rate)? Plenty of people I know started out using regular pot cubes and the rate for unique -> legendary was bad throughout the event.