Interesting - was thinking about fares from AMM, but this has some attractions, albeit burns two euro segments.
a 2006 FT post talked about a 6-hr visa but I can't find any recent web references and the page at the Sudanese US embassy no longer exits
unsure about KRT (would suggest emailing the airport or Sudan UK or US embassy), but have done a similar 2-hr turnaround in KHI - airport layout there was a single level airport - had CX staff meet me at gate escort me to lounge, take passport to front desk, and come back with my ticket
I also note this review:
http://www.sleepinginairports.net/af...um-airport.htm