The way I was taught--
It doesn't matter whether you shrink or stretch. But you do need to pick the recorder which has the best time clock as your base.
Line up the files near the beginning with a sharp note, bass notes don't work so well.
Go out 30-45 minutes and select another sharp note and drop another marker on the two files, separately.
Get out of the digital time mode and display samples.
Subtract the difference in the samples between the two points and get the percentage, whether it is .999875 or 100,00123 Doesn't matter. Stretch or Shrink
Time digital display is not accurate enough
I find working with most DAWs for this project to be annoying because when you place a marker, it does across all the files, which is not useful for time alignment. So I use a two channel waveform editor to place the markers and go back and forth between the waveform editor and the DAW multi-track. Adobe Audition either cc or 3 has some advantages in this regard in that it combines a two channel waveform editor with a multi-track and you can seamlessly pop between the two.
Repeat the marker drill every 30-45 minutes.
Problems may surface when the recorder malfunctions dropping a section even ever so small, and finding those write errors is, well, I just don't have the skill set to do that.