Found it : I had used an abbreviated time format "index 01 00:00", it needs another ":00", this one here works :
performer "Dire Straits"
title "Live In New York"
file "Dire Straits - 1992 - LIVE in New York.aac" aac
track 1 audio
performer "Dire Straits"
title "Calling Elvis"
index 01 00:00:00
track 2 audio
performer "Dire Straits"
title "Walk of Life"
index 01 12:38:00