How long should I charge my new iPhone 5?

I just got my iPhone 5 today. However, my parents want me to charge my iPhone with at least 24 hours (without doing anything to it). They believe that charging phones long enough for the first time will prolong the battery life.
However, I tried to google the answer and people said that lithium plasma battery does not have to be fully charged for the first time. I also know this is true because my AP Chemistry teacher once told me that these kind of batteries don't have to be fully charged.
But anyway, I just want to ensure that it's okay to NOT charge my iPhone for 24 hours.
I don't want to damage my iPhone because of the battery. I feel like I need to ask this question because, not just my parents, everyone said that you need to charge your battery for a long period of time for the first time.
Please give me some PROPER recommendations on charging my iPhone.

Just when ever it gets to 100% and when to charge it is when it gets to 20% and let it completely die one time a month.