Reynolds is also an astrophycisist, so he applies relativity quite consistently. A journey that takes a decade or two of "outside" time may only take a few years "ship" time.
This has the interesting side effect that ship crews (who don't go into cryosleep like their passengers do) have become their own isolated culture, the Ultras. Many of them are several centuries old in planetside time and basically never leave their mostly empty ships.