It looks like a mistake that wasn't corrected by the editor before publishing. Perhaps the writer was considering writing "then held for at least two hours" but decided to write "about two hours" instead, forgetting to delete the "at" . Your English must be good to notice something small like this as not looking right. I am not American, but I think that FLL is the airport code for Fort Lauderdale airport. Just like how LAX is the code for Los Angeles International Airport. The other sentence you referred to is also poorly written and similarly could be due to the writer changing their mind about what to include in the sentence. "A federal judge blocked the order days before Ali Jr. was detained" or "The order was blocked days before Ali Jr. was detained" would probably have been ok, but was was written is not. I guess that is one of the problems with using Twitter and online news sites, they are likely to contain more errors due to a lack of oversight by an experienced editor and the demands to publish stories as quickly as possible.

The first 'at' is a mistake. It shouldn't be there, it's wrong. FLL is the code for Fort Lauderdale airport, where he was held.

The first AT is an error and should not be there. FLL is the IATA code for Fort Lauderdale-Hollywood airport. Beijing Nanyuan Airport = NAY and London Heathrow = LHR. The second query is also an error. It should read: A federal judge blocked the order days before Ali...

For the first one, it looks like there were some missing words. I think it should read: Muhammad Ali’s son was questioned twice about his religion, and then held for at *AIRPORT FOR* about two hours at #FLL. https://t.co/y7SBEBQq49 I think #FLL is the Twitter hashtag referring to Fort Lauderdale airport, where the incident happened. The second one is a typo.