Yea I'd say 4-5 hours should be good, it's different for every person. Play around with it and once you have success you'll know about how many you need. If you wake up and can remember a dream that is really fresh on your memory you should be good.
I strongly recommend meditation. WILDing and meditation are very similar, I sometimes describe it as 'meditating yourself to sleep.' When I had my first few WILDs I was meditating almost every night.
Also, don't be discouraged if you aren't having success early, WILDing isn't very easy to learn(for most people). It took me months to have my first WILD and a couple more months to get them somewhat consistently. As long as you stay determined and dedicated to practicing you WILL eventually have one.
I don't know if you have seen these or not, but I think these are two good guides to read for some pointers.
How to Lucid Dream - Dreamviews Lucid Dreaming Community & Resource
http://www.dreamviews.com/f79/mzzkcs...-guide-105484/
Good luck! Happy dreaming