ATL Transfer in two separate tickets
 

As far as I searched for my specific travel dates, IST-FRA-ATL on Lufthansa Y is almost €400-500 cheaper than all airlines's IST-XXX-IAD flights where I intend to buy an American Airlines ticket for ATL-DCA. I have the option to have a 2h30 connection or a 5h one, if I choose AA Y ( would be Main Cabin Extra for free ) for the next leg. ( AA is my top priority because I will 2 have 2 checked bags which would be free for me depending on my OWS status ). The other option is to buy Delta First ( which has a $80 difference than DL Y which would waive 2 checked baggage fees); the Southwest ATL-DCA schedule does not fit to me and DCA would be my preference as I would pay more if I choose Spirit to BWI buy paying extra transportation + 2 checked bags + a carry on. I don't consider UA to IAD as an option.

So If I want to do something like this, how much should I allow for a passenger responsible transfer. Would 2h30 mins be fine or minimum 3h30 mins or maybe more?
I am considered as a Visitor and my visa type does not allow kiosks, mobile passports, Global Entry etc... so I must clear immigration at a staffed desk.

Thanks in advance;

Given that you will be on two separate tickets, and will have to check your bags in at an AA ticket counter at least 45 minutes before scheduled departure time, I would give myself more time -- not less time -- to make the transfer at ATL. But does going via ATL yield the lowest total cost for both tickets? Have you priced things via other North American cities, like MIA, MCO, JFK, BOS, ORD, YYZ, YUL?

This is all about your risk tolerance. Nobody here can predict what will happen with your inbound flight on the day of travel. If it is delayed and you no show for your onwards ticket, you will either be required to purchase a new one at walk up prices or hope that some agent is merciful.

Typically an offline I-D connection at ATL would be 90 minutes. As a rule of thumb, I would allow 3x that or 4-1/2 hours.

Well, AA does have an informal "flat-tire" rule, so that if the OP were to miss his ticketed AA flight by an hour or two, he would likely be re-accommodated -- at no additional cost -- on AA's next available ATL-DCA flight. The problem, of course, is that the next available flight will not necessarily be on the same day!

And if the OP's LH flight were substantially delayed due to mechanical or personnel issues, he would be entitled to EC 261/2004 compensation -- which could go a long way to offsetting the cost of a last-minute ticket on a different carrier.

It looks like the OP, as a oneworld Sapphire elite member, is entitled to free same-day standby on AA flights -- no flat-tire rule or agent mercy necessary:

https://www.aa.com/i18n/plan-travel/...day-travel.jsp

​​​
I would probably book the later AA flight, and if I got through Immigration and Customs quickly enough, I would try to standby for the earlier AA flight.

Thanks all for your help and advise;

ATL or TPA is the only airports which has the lowest fares and a reasonable connection time for my specific travel date.
Unfortunately, none of the east coast destinations and Chicago & Detroit had the same low price. I haven't checked MCO as it would need a 5h+ wait time in FRA and I haven't also checked YYZ or YUL as I won't have a Canadian visa ( I require a visa due to my nationality ) for my travel dates.

Yes, I am probably going to buy the later AA flight if I pass through CBP quickly, I would try to go to the standby list for the earlier AA flight. Sometimes, a free same day confirmed change worked on AA for me when I requested it at one of the service desks at the Admirals Club.

Yes, I usually allow minimum 4h for this connection. I won't risk it to 2h30 min. It's impossible to estimate US CBP wait times. Btw, thanks for the advise.

My one issue with Atlanta would be you would arrive at F but then have to get back over to the domestic terminal to check your bags in with AA, which would require a shuttle bus. Tampa might be an easier airport to make such a self-connection.

Thanks again for all of you again, I have found a same price discounted ticket ( IST-FRA-MIA on LH ) and ( MIA-DCA on AA ) for the exact same price; I would consider transferring at MIA even though I would fly hundreds of extra miles. At least, I could walk from Terminal J to Terminal D in Miami. At least MIA immigration is fast for visa-holders as they have designated immigration counters and officers which is empty or less crowded most of the time.

All other factors being equal, I would rather go with a smaller transit airport, i.e TPA. MIA can quickly turn chaotic, if several international flights should arrive at about the same time.