"Duo is going south during the fall."
Translation:Sonbahar sırasında Duo güneye gidiyor.
Not here. I don't know if duo differentiated between them but 'sırasında' indicates that something is happening or being done within a period of time. It can be summer, holiday, party, january etc. Whereas 'boyunca' indicates a process of action.
'Sonbahar sırasında Duo güneye gidiyor.' means that Duo is going south within sometime in fall.
'Duo sonbahar boyunca güneye gidiyor.' means that Duo is going south during all autumn which is odd and illogical.
But it can be used in a sentence such as 'Duo sonbahar boyunca okula gidecek.'(Duo is going to go to school during the fall.)