How does investment horizon change duration risk?

The horizon determines whether price risk or reinvestment risk has more time to affect realized return. If the investor sells before Macaulay duration, the immediate price change usually matters more. If the investor holds longer than Macaulay duration, coupon reinvestment can become more important.

So rising rates are not always purely bad for a bond investor. They reduce the bond's current price, but they also allow coupons to be reinvested at higher rates. A long enough horizon gives that reinvestment benefit more time to compound.