It depends on you background on your english and also you capacity to remember the words. If you english background is average, then don't give any bit of time solving passages. At this time no matter how much time you spend on passages its very difficult to improve passage solving as it totally depends on your background in english. Spend all time in learning word meaning, not only those of barrons, also others. The advantage is that if you could remember lots and lots of word meaning then you can easily solve antonym parts, word pair match and also will help in solving sentence completion. So fact is that you should know as much words as possible. So it is not related with you english background to learn more words. It will greatly help in scoring. To be honest I did the same, I ticked all passages questions with guess ( Among 3 passages I read only one short passage and didn't go through any other passages because I was poor in grammar )and some sentence completion questions with guess. What I did with confidence was antonym and word pair matching which I got all right. and I scored more that 550.

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Reading passages is a long-term skill that depends on your background in English, and like guest 4 suggested reading current literature is the best way to prepare in addition to taking practice tests from gre books.

Here is one strange way of memorizing words if you are having problems. record the word, its meaning and  a sentence using the word on your tape-recorder/ipod/mp3 player whatever you have. whenever you are free, just play it over and over again. trust me the words will be "ingrained" (its one of the 500 gre words by the way) in your memory. its like listening to a song...it worked for me, Hope you will finf it useful.

If you dont have great command over vocabs, and pretty average reading skills by Gre standards, you will need more than 2 hours a day for sure. i would say at least 4 hours. G'luck