Hours at visa window @ Istanbult Airport

From the US Dept. of State website, the IST airpor website, the Turkish consulate, website, and especially this forum, I've confirmed that for US citizens, it is not necessary to purchase a visa in advance and that one can be easily obtained for 20 USD at the IST airport, just before passport control. The price difference is huge 20 USD upon arrival vs. 60 USD consular fee + 55 USD for a local passport/visa agency to help you obtain it (110 USD x 2 travelers). However, one piece of information I have not been able to find or confirm is whether the visa window @ IST has closing times. Our flight arrives at 4PM local time on a Sunday. I just want to make sure that the visa window is not closed when we arrive. Any advice is much appreciated!

The visa window is part of the immigration process. If there's a border guard there to stamp you in, there'll also be one to sell you a visa. Just make sure you have cash in $ or € to pay for it. I arrived in Turkey by bus during the day, but in other countries with similar processes, I've been known to buy visas at 3:30 am.

Thanks.

I did some searching on the net and found this site:
http://www.letsgoistanbul.com/before.htm

According to them, the visa window is open 24hrs. Regardless, it stands to reason that it would be open anytime flights are coming in.

I was there in April and there was absolutely no issue or fuss getting the visa there- you hand over your money (cash in USD is accepted) and they put a sticker in your passport. That's it.

Customs can be long at the airport but that's another matter.