I checked the thread where those numbers came from, and it had a link to another thread where there were equations to calculate relativistic effects. Unfortunately, the link was dead.
If interested to “drill” further, there must be many alternatives to search for. Online plug-in calculators and the like. The sites themselves may come and go, depending on the funding behind it.
It makes sense to me - time dilation is a proven real thing. Fascinating to the imagination, obviously this ‘aint happening anytime soon. You can travel at .95c, but getting there will be a hurdle!