I am traveling with my family to Spain for 16 days in early June. We are traveling from Anchorage and by far the most efficient way to get to Europe from here is a direct flight from Anchorage to Frankfurt on Condor, and this flight is already booked round trip. Unfortunately, there was no way to combine this booking with flights into and out of Spain (we want to start in Barcelona and finish in Madrid) into a single booking without exorbitantly expensive options. As such, I will have to book separate reservations for those flights. Obviously this adds some complexity as we will need to clear security and customs in Frankfurt, get our bags, and check in for the flight to Spain before going back through security. Similarly on our return flight we will have to get bags and recheck for our flight back to Anchorage. For those who have spent a good deal of time going in and out of Frankfurt on international flights, how many hours should I allot for this to play it safe?
I have done this sort of thing a few times but not via Frankfurt; I've done it via London, Paris, Amsterdam, and Madrid actually (easy for me to get a direct flight to Madrid, on the way to somewhere else!). There is a risk of course that you will miss the connection if your incoming flight is late. Obviously, the more time you leave between flights, the less your chance of missing the connection...but too much time, and you waste a lot of extra time at the airport etc. Some people would even stay overnight on each end to minimize the risk, though I've never done that unless I couldn't avoid it.
First of all, you need to look at contingency plans in case you miss your connections. I'm guessing the penalty for missing it on the inbound is worse than missing the one home, because buying a last-minute ticket to Anchorage from Frankfurt would probably not be cheap! So unless your Condor flight home isn't until the afternoon, I might consider spending the last night in Frankfurt. Otherwise, if the Condor flight home is in the afternoon, if there's an early flight out of Spain to Frankfurt, just take the earliest one you can get. Up to you how much you want to push that as far as risk.
The inbound might be less risky - at worst you'd have to buy a last-minute ticket from Frankfurt to Madrid, which may be a lot cheaper than an international Condor ticket back to Alaska on the other end. You might have a bunch of direct flights to choose from from Frankfurt. I'd probably give myself at least three hours in between - maybe more if there aren't many direct flights on to Spain after the one you would be booking or in case it might be crazy expensive. (Try this: what's the cost to book a last-minute flight right now to fly TOMORROW from Frankfurt to Madrid?)
In any case, just know what the risks are and what the cost is if you miss your connection - and be prepared to pay it or live with it if you miss it. If you aren't prepared to do that, then be safe and spend the night each end of the trip in Frankfurt and connect the next day.
There is some chance that trip delay insurance (some credit cards offer it if you book your travel with them) might cover the cost of missing a connection. Call the insurance company and ask if this is an option for you.
Condor nonstop flights from Anchorage are scheduled to land at Frankfurt at 1:10 pm. Looking at Lufthansa nonstop flight to Barcelona, you have your choice of 4:00 pm, 5:30 pm, and 9:05 pm. 4 pm seems risky, 5:30 pm less so, 9:05 pm the safest. If your Condor flight is delayed, and you miss the separate Lufthansa flight, you could be on the hook for buying an entirely new Lufthansa open jaw trip ticket at last minute prices. For the return from Madrid, you have the choice of 6:10 am or 8:30 am. 6:10 will definitely be safer.
As I see it, you have gotten a round trip to FRA for $839 plus an open jaw FRA to BCN and MAD to FRA for 178 EUR (~$200) plus luggage fees of another ~$100. So that would be about $1189, Condor is offering that ticket with guaranteed connections for about $1210, so this way you are saving $20 but taking on all the risk of a missed connection. You say you already booked the ANC-FRA round trip, so I guess its water over the dam at this point.
I picked random dates in June, on the condor, site and produced a single booking using the multi city feature-- Anchorage to Barcelona/// Madrid to Anchorage for ~$1200 rt. Is that ' exorbitantly expensive' ? Given the distance covered it seems reasonable to me. The rt cost Anchorage to Frankfurt was a bit over $900.
The other flights to/from Frankfurt will cost something so when that is subtracted any positive number is the cost of peace of mind and convenience of not retrieving and rechecking luggage and the 'what if' if you miss the flight.
As you are planning it, I would be uncomfortable with less than 4 hours going and 3 hrs on the return. ( no personal experience in FRA)
As a single booking condor has a 90 minute layover time for Anchorage to Barcelona through Frankfurt.
I should clarify that we have business class seats for the Condor flights, and I was not able to book these business combined with intra-Europe flights in economy on the same reservation. The way prices worked out, I would've been paying about $1000 per ticket for the flights to and from Spain (out of and into Frankfurt) with a combined reservation and all the flights in business class, versus paying about $80-$100 per ticket each way by booking them separately in economy. All in all, booking separately is certainly a risk but in this case saved me a good $2500.
What's the earliest flight out of Frankfurt to Barcelona? Your first day is lost to jetlag anyway, seems to make sense to spend the night in Frankfurt - think of it as an opportunity to have a look round at a pretty city center. Then you get to Barcelona after a night's sleep and only lose a morning in Barcelona. There are hotels 10-15 minutes' walk from the Frankfurt train station, then a 15 minute train ride to the airport.
I looked at the flights, looks like you have a return flight at 2.35 pm from Frankfurt. Since your morning is lost anyway, you could take late evening flight back to Frankfurt, again overnight near the train station, then have a leisurely breakfast and a walk before heading to the airport around 11.00 am to be there 3 hours in advance.
Frankfurt train station has luggage lockers, so you can stow your stuff there and need only small overnight bag both coming and going.
I've only been in to Frankfurt once. In the spring of 2018 my overnight Lufthansa flight from IAD (Washington, DC) to FRA was scheduled to arrive at 8 am and our booked-on-the-same-ticket flight to Barcelona was at 9:40. We breezed through immigration, then had a long march to what felt like the other end of the planet (my notes helpfully say gates Z69-A36) dragging our carry-ons. We didn't go through security and the checked bag went straight on to Barcelona. The flight must have been on time or perhaps early as we had time to stop at an ATM and to purchase and eat muffins and coffee. But if I were you I'd follow the suggestions of previous posters with more experience, mine was really a best-case scenario.