It depends on how fast your lips dry out or how dry they are... I tend to have lips that absorb quickly and I found I was reapplying ever couple hours but my best friend could go for twice as long before she needed to. Hope that helps!
It's balm, not a long wearing lipstick. So yes, of course you have to reapply. Not only to refresh the colour (which is just a tint) but also to moisturize your lips and protect them against the elements.