Does what take? C-mode?
Challenge Mode is many stages with their own timeframes. Episode One has 9 stages which will last approximately 4-6 hours (Sub 7 for srank weapon) and Episode Two has 5 stages which will last approximately 3-4 hours (Sub 5 for srank weapon). This obviously depends on your parties size, class, skill & knowledge of cmode. You can do a stage at a time, the longest ones being around an hour at a slow time. And many shorter ones around 30 and below.
As in 10pm-3am GMT? If so see you tomorrow