26 hours in Seoul/Inchon-DMZ tour?

The USO tour goes at 7:30 am, and most of the Korean day-trips shortly after.

Customs in Incheon can be anything from 10 minutes to 70 minutes. A direct train now runs from Incheon to Seoul Station, & is cheap & fast. Get the 'all stations' train which is 1/3 the cost (4k instead of 12k) & only a few minutes slower than the express. Takes under an hour. Buses sometimes take 2 hours if it's raining & traffic is slow. From Seoul station turn left just before you exit the main door & go down into the separate subway train system, for Line 1 to Jongno Sam Ga. Unlike China, Koreans queue and it's not a problem with luggage. Google 'Seoul Metro Map' or subway.

Seoul has a safe & efficient metro system so you can stay in any district. Jonggak is good as it's near Insadong & Gyeongbukgung Palace. Others prefer Myeongdong.

Actually, I just got the updated DMZ schedule sent to me yesterday from Koridoor and their tours go at 12.30 on Wednesdays so if you arrive on a Wednesday you'll be fine.

that's the other problem. I get in on a Saturday morning.

Some tour operators have both morning and afternoon tours.
You should be aware though that Inchon is a huge airport and any travel to a place outside the airport takes about an hour or more.
If you have booked your accommodation in Incheon or Seoul, the hotell staff might help you with advice and booking (if they speak English).

I havent booked a hotel yet. I was waiting to see where i needed to be for a tour since that is the number one priority. All the "afternoon tours" i have seen start at like 10:30 or 11

It's Incheon, not "Inchon" & it's one of the best airports in the world.

"Following the opening of the second phase, Seoul–Incheon International Airport travel time on half-hourly express services is 43 minutes; while commuter services, which run at a frequency of up to one train every 6 minutes, take 53 minutes.[9] This competes against a theoretical travel time of 70 minutes on buses, 60 minutes on taxis, and 60 minutes with private car."

That 43 minute train is like 13k won & the 53 minute train is just over 3k won. Still quicker than the bus. Ignore taxi drivers that try to pressure you. The bus is a good second choice except during peak hour or rain.

http://en.wikipedia.org/wiki/AREX

Incheon has been voted THE best aiport in the world for second year in a row.
Incheon or Inchon, it's quite inessential. 'Incheon' is an attempt to adjust English pronunciation and spelling to Hangul, and that might be right or wrong. Anyway, the pronunciation, and the old spelling, is Inchon.
Seoul used to be spelled Seul, or Sëul. Daegu is spelled either Daegu or Tegu, Gyeongju can be spelled Kyongju, depending on sources and how old they are.

Back to topic...
OP, tour participants are being picked up from their hotels. You might try and ask a couple of tour operators about their route from Seoul to DMZ, and ask them to suggest a hotel where they'd pick you up. Maybe in Gimpo (alt. spelled Kimpo), which is closer from Incheon. You can get to Gimpo by direct train from Incheon airport.
Just a suggestion...

I know all about Korean spelling. I lived there for 5 years! You forgot Pusan / Busan