You can try as soon as you want to. Initially, the specific time is not important, but more like the intervals (eg. Baby should only be awake for about 45 minutes each time during the day) and the way things are done eg. Pre-bedtime routines. Feed on demand first, then gradually you can stretch the feeds out
I set my baby sleeping routine as young as 1 month old.
Started as soon as nanny left
Right after 1month for my boy