Time is a finite resource. No matter who we are, we all have the same 24-hours in a day. Rich, poor, famous, obscure, smart, stupid, black, white—it doesn't matter.
Money, on the other hand, is a comparatively infinite resource—although we tend to ascribe it more value that is really has. We see it as all-powerful and difficult to obtain. In western culture, we put money on a pedestal. Certainly, money is a useful tool for day-to-day living and expediting progress, but it is not the be-all, end-all.
By this comparison, our time is actually more valuable than our money. We can always earn more money, but none of us can create more minutes in a day.
When someone, then, asks for our time, they are asking of us our most precious commodity. How we spend our time and who we spend it with should not be taken lightly or treated casually.
When you give a friend "only" your time, you are giving them a gift greater than any sum of mere money.
Your time is priceless. Use it well.
To your good fortune!