Appreciated guys, can't believe I missed these! Also got a bit confused with getting getSampleLength and getSampleRate.
Case of the mondays I guess.

const var SamplePlayer1 = Synth.getAudioSampleProcessor("SamplePlayer1");
const var audioFile1 = SamplePlayer1.getAudioFile(0);
const var samples = SamplePlayer1.getSampleLength();
const var sampleRate = audioFile1.getSampleRate();
const var lengthMs = (samples / sampleRate) * 1000;

Thanks again.

Hey all.
I'd like to get my wav file's length in milliseconds. I can do sample.getSampleLength() and get the length in samples and then do:

var ms = (samples/samplerate) * 1000

However, how can I get the samplerate of the wav?