When is it safe to leave my baby alone in another room for a few minutes?

As soon as you want. Delivery begins a new stage in a kids life marked by gradual aquisition of new talents of independent living.If you have prepaired a safe sleeping area for baby at home, there is no reason not to leave them alone in that area as soon as they come home. You may desire to monitor their activities closely, but close monitoring can prevent restful sleep.
See below. Put the child in a play pen, such as a pack and play. This will ensure they cannot get into anything they shouldn't. However, even with this you need to be vigilant.