it solely depends on wen u wanna giv ur gre xam...lyk if u r goin to giv ur gre nxt yr, arnd jun-july..den as for nw thr's no need f memorizing words...yes bt its better to start wid ur vocab part nw...lyk u cn go thru wordlists evry 1 or 2 days...to get familiar wid difficult words
bt in d end u hav to mug up ol d wrds...so it depends upon one's retaining power...it takes arnd 2 n hlf mnths approx(provided dat,u r paying less attention 2 ur academics)..to prepare for ur verbal section(dat includes ol d sections f d verbal)....so its advisable...to memorize d wordlists 2 mnths prior to ur date f gre xamination...