About that, there's lots of youtube videos, but this is an old bug fixed in the most of servers.
All I know: the door of zaken can be opened from 0.00 to 0.15 time on-game; buff your self with holy weapon + dance of light; use a destroyer lvl 61 and a dagger pg and, if possible, take a bishop with you; be careful 'cause Zaken's hits have a little possibility to teleport you in a random lvl of his boat. ;)
PS: about the last thing, if possible take a WC and use his gate chant for re-port you on the right place...
Ps2: take zaken out from his hall. When is out, let him follow you in a safe place (take a tyrant in rabbit totem + DEX dye + Light Armor) in pirate island. Then die by his hits, is indifferent. Respawn in town, take a gate port by someone in the place where you have leave Zaken and w8 the in-game daylight. When in daylight, zaken is more weaken and regenerate him-self more slowly / drain you more slowly.