Granular Synth Playhead Time node : seconds or sample rate?

Hey there!
I’m having fun using the Granular synth.
But it seems that the node Set Playhead Time doesn’t work as intended. I have for example a bit of a track that last 64 seconds at 120 bpm.
If I set Playhead time to 32, it doesn’t actually play the grain at 32 seconds.
Do you have an explanation why?
Also, If I print with get playhead time at 1 second, I have the value 48000. So Set Playhead Time, is it in seconds or Sample Rate?