Do it now. The best time to meet a friend for lunch is before your baby is mobile, while he's still content to chill in the stroller or on your lap.
Go when your baby sleeps. Don't be surprised if your baby falls into a deep snooze thanks to the calming rhythm of being rolled around. "My husband and I would take our son out in the stroller when he was tired and in two seconds he'd be out," says Caroline Bollinger. "Then we could go to lunch, grab coffee, or shop -- the freedom was great."
Stay flexible. I remember abrupt ends to coffee dates when Lucy became fussy, but that was okay. To me, some time out was better than none. And try to avoid places that may be too stimulating for your child. Lucy hated the bright lights of the mall, but your baby may love it. You'll just have to try and see!