Short answer: take whatever conservative time estimate you have and double it. Take at least twice as much water as you think you'll need too. Unless you're cheeky and optimistic about your water consumption like me, in which case... take three times as much!
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NW Lake Gordon/Pokana Bay to Pokana Peak itself is deceptively steep, very scrubby in many places and - this time of year especially - likely to be very dry and hot. It's slow country to move through, especially heading up. Don't underestimate how energy sapping buttongrass is in the middle of summer.
Be aware the current lake level is lower than what's shown on any topo map. That's an extra 1-3km of walking, already, depending on what direction you head in.
Most people who come in from this direction (apparently the minority, most come in from the Denisons) seem to go up at or just north of The Pleiades ridgeline and follow the ridges to Pokana. Access to water this way would be a big concern. We tried heading up a bit further north and only found one good water source the entire way. Ended up having to turn around a good 2km from the summit due to lack of time/light.
Our second attempt we headed straight north towards the summit then used a ridgeline to the SW. We were successful but it took almost all day to get to the summit - with a smaller, strong, determined group and more mild conditions too. We ended up bivvying halfway down on the way back after exhaustion and hours bushbashing in the dark got the better of us.
Best to not be tempted by the ridgeline directly south of the summit or its eastern flank. Apparently one or two crazies have managed to descend it, but it's very, very steep, very cliffy and likely to be some combination of extremely difficult, impossible and dangerous to attempt to climb.
Can't offer much advice beyond Pokana itself. Check out the NatureLoverWalks and Rock Monkey blogs. Mouser on YouTube did a Pokana Bay-Denisons loop trip recently too.
It's a beautiful place, but it makes you earn it every step of the way.