boguing,
I took the tablet at the supplier I acquired it from, some 27 hours after the last change of password. He just switched on follow the steps the same way I did but this time it worked - as he was allowed to proceed where I was turned back to re-enter the gmail account and password.
I asked him about the 24 hours wait period but he did not really know it. What was interesting was his comment that a repair after a factory reset and cache memory clearing which led to problems is covered by warranty in 99.9% of cases. So there is hope for your issues.