A little while ago I was contemplating the effect of time dilation and worked out what the effect would be on a ship traveling at various speeds. To my surprise even the (what I thought to be a fast speed) 140 miles per sec linear velocity that the sun achieves going around the milky way isn't making any effect - that is if you consider that less than 18 seconds per year is tantamount to having no effect.
In fact it isn't until you fly at speeds close to the speed of light that the time dilation effect shows any real difference.
EQUATION = 1-(V²/C²)
or in plain language = '1' minus (the velocity squared of the object to be calculated - divided by the velocity of light squared)
100 miles/sec = a factor of 0.999999711 Virtually no time dilation.
100,000 miles/sec = 0.710949243 (or 29% slower) ie 100 years would go by in 71 years on a space ship.
150,000 miles/sec = 0.349635796 (or nearly 65% slower) ie 100 years would be nearly 35 years on ship.
185,000 miles/sec = 0.010723783 (or over 99% slower) ie 100 years would go by in 361 days.
185,999 mles/sec (just 1 mile per sec below the speed of light) means that 1 year would go by on Earth whilst the ship would only have been flying for 5.65 minutes.