Q:

Why do mp3 files have a time delay when compared to wav files?

At first I thought this was a tempo issue when exporting my stems from fl studio to cubase. But when I zoomed in close enough and lined up the tracks they were perfect (ie. no stretching). The mp3 master track seems to be delayed by about 30 ms (ie. 30 ms of emptiness at the start) as compared to the separated, mixer tracks in wav format. Why is this the case?

A:

Here is a relevant answer/troubleshoot steps to go through. This is an excerpt from x42 posted in Ardour forums:
"First thing to check: is everything in sync on your machine before export?
Next step: re-import the exported file into your session. Does it line-up 100% ?
(check visually and/or invert the polarity of the imported ones (mixer phase invert button) the sound will cancel out if they're 100% aligned)
If both are true: then either
(A) your session was not in sync with the other when you started recording
(B) the file is not imported at the correct position in the other DAW."
The thread (linked below) raises some good points. One thing you could try doing is setting a track delay on the wav channel within the DAW to create a set delay, since it seems you know the exact amount of delay happening. 
Link: https://community.ardour.org/node/8591

