That is assuming the objects will be at the same place relative to us, which is not true. Like reaching Andromeda. Voyager I will reach oyr neighbouring galaxy in roughly 4.5 billion years, not 45, that's because Androneda is moving in our direction. Reaching Proxima Centaury would take longer than your estimation because of it's orbit around Alpha Centauri A/B.
Estimating time-to-arrival when your destination is also moving at ludicrous speeds is incredibly difficult.
Estimating time-to-arrival when your destination is also moving at ludicrous speeds is incredibly difficult.