I hope the reduction of the mobs is not based upon the number of attacks from players.
Using 9 hours as best time case and everyone starts another attack as the last one ends:
7000 x 9 hours(min) = 63,000 hours required
63,000 hours / 100 players = 630 hours / 168 hrs per week = 3.75 weeks
63,000 hours / 375 players = 168 hours / 168 hrs per week = 1 week
I think we need to get a clarification from Uiqua about this especially if there is a time limit of 1 week. In that scenario, it would be highly unlikely all the mobs will be defeated on this server. And if that is the case, we are just wasting resources and missing dungeons for no reason.
As of right now the mob count is only reduced by 44. So maybe 50 players participating:
63,000 hours / 50 players = 1260 hours / 168 hrs per week = 7.5 weeks
I really hope either the mob counter uses a much different algorithm or my math is just wrong.