Well, I am not a mommy, but I am going to answer anyway!Lol.
I feel that it is okay whenever you are ready. Because if you aren't ready, you will know, if he isn't ready you will know, and if you have someone that you really trust to leave him with then it is no big deal. You do need some alone time, ya know.
Overnight is a different story! Everyone I know who has kids didn't leave their baby with someone else overnight for a long, long time! Too hard!
But anyway, yeah whenever you feel that you are ready is fine.