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.