Unfortunately I can not give you the exact time it occurred. I was concerned it was the fraudulent site and removed it from my history. I can see the space where it was.
I had begun a Finito game at 12:37 AM EST. When it ended I returned to the main menu and got the offer. Clicked on it and then happened as I described above. I closed that page, went back to Happy Meeple, got the offer again, and the same thing occurred.
At 12:43 AM I went to the Happy Meeple forum to post the info. So it occurred someplace between the end of the game that began at 12:37 - I'd guess it took about 5 minutes to play the game. That would bring it up to about 12:42 when I tried to get the reward. I'd like to repeat that I am in the US Eastern Standard Time zone. I think this is about 5 hours earlier than the Happy Meeple time.
Also, after I finished posting. I closed the browser, reopened it, and went to another site, because I often can not get into Happy Meeple right after leaving it. When I came back later, I was able to get the reward with no further problems. That was at 1:35 AM US-EST. So closing, and reopening the browser might have cleared the problem.