I voted for option two. BUT i think it needs a blend of Option 2 & 3... Definitely far in the future, keeping with the advancement and spread of the infection. and the virus evolving and such. example is smarter zombies... ect. and since there are new areas in SA it gives the lore a chance to expand and and create new opportunities in the world that isn't in the mod. another example is the new bases and towns that tried to build and civilize but failed. Like if your group has survived this long, i think it deserves to "stay around" 5-10 years later.
During that long period, some good theories can be created to help with the drastic changes from the mod to SA.
*grabs his two cents from his pocket and pushes it in the machine*