The dev team were not going to go with an 18min duration (as was), as this just means a slightly uncomfortable version of a permanent effect. I remain utterly unconvinced on a 12min duration for the same reason.
Also, 12mins would require an extended displacement with a caster level of 60, unless i very much miss my guess. Let us not forget that even before the arcane rework an extended displace lasted 528secs (8.8mins) with a max CL of 44.
Trying to keep this in perspective, the other melee set 'clickies' (that i can think of, correct me if i'm wrong) are as follows:
Black Guard - BAB 40, +12STR, +18 dmg, 60% conceal for 1min; 2/day
Paladin - +500hp, regen 20, Ethereal for 30secs; 3/day
Fighter - 50/DR-, 75% conceal for 1min; 3/day
Swash/Thug - 85% conceal vs ranged only +300hp for 2mins, regen 60 for 30secs; 3/day
Eldritch Knight - +5AB, 75% conceal for 1min 30secs; 3/day
Dwarven Defender - Barkskin/Regen Spell CL 13 ;3/day
Rogue/Monk being +8 AB, 60% conceal for 3mins and regen 20 for 30secs; 2/day seems pretty darn strong in comparison.
As Monk is now a full BAB class with access to EWF and Rogue set has a passive AB boost to make up for med BAB, I can't see as either require a semi-permanent +8 AB. There are also several methods of obtaining a displacement buff: droppable items, pandora's/sequencers, scrolls, party members; if you really feel you need it for a difficult area and the cloak plus resting isn't enough.
Not to mention the fact the duration was a developer error in coding, it was never meant to last that long - and this is the real crux of the matter for me personally. Every time a dev does anything there is a chance of an error that under-powers or over-powers something. If every time it over-powers something, the call is 'keep it and raise everything else!', then that is an enormous amount of dev work - there are simply not enough devs, or time, to do that. Would you want to do that? You make an error and suddenly you have tons more work to do; far, far more than just correcting the error would take?
If an error is made you fix it, you don't re-write the system to accommodate the error.