Unlike NIMH, LiPo have very low self-discharge, you can charge it a few days before using it and it won't have have lost more than a few percent charge.

You want to avoid storing it fully charged or fully discharged though. If you are going to store it for more than a few weeks, discharge the pack to around 40% charge. They degrade over time and it's roughly 4% permanent capacity loss per year (if stored properly) but as high as 20% permanent capacity loss per year if stored fully charged.