Without getting too deep into this issue of relativity, let me point that that the Milky Way is per Wikipedia "100,000–120,000 light-years in diameter".
Rather than go down to Planck level granularity, if reaching space flight, or better, serious engineering works in space that are visible from afar is a low probability thing, with time scales say in the millions of years, then "first" will I think do for our purposes.
Rather than go down to Planck level granularity, if reaching space flight, or better, serious engineering works in space that are visible from afar is a low probability thing, with time scales say in the millions of years, then "first" will I think do for our purposes.