Matching Time || Missions || Instance Dungeons ||
5 Mins || 10 Levels || 20 Levels ||
5~10 Mins || 15 Levels || 30 Levels ||
10+ Mins || 20 Levels || 30 Levels ||
Source: (Translated Korean PatchNotes)
http://pastebin.com/uPq3hQXm
Hope this helps you guys out having issues with missions and dungeons.