Waiting a couple weeks is REALLY common (working in a women's clinic we'd have a lot of paperwork with BabyGirl a. on it). It's not as common as it SHOULD be though. I don't know the stats on it, but I knew soooo many families who changed their baby's name in those first 6 months (it's free and "no court" to change a baby's name in the first 6 months/ a brand new "original birth certificate" gets issued, instead of a name change certificate). To a family they all had names picked out, but when their child was born it didn't feel right anymore, but they didn't want to leave with the pretend-certificate blank (you don't get a real certificate anymore). So after a few weeks, they said 'screw it, he's an Ian, not a Michael" and changed it.
My friend's parents waited 2 months to name their eldest for very stressful reasons I won't go into. He'd been "BabyBoy a." for so long, that's what they used as his middle name. (making up a first and last here) so he became John a. McCaffrey. Then they kept up the trend.
John a. McCaffrey
Ian b. McCaffrey
Shane c. McCaffrey
Aoife d. McCaffrey
Niamh e. McCaffrey
For myself, I knew my son's name before I knew he was my son (sex undetermined), and it fit him when he was born *perfectly*. But if I'd had a daughter, I'd have been screwed. COULD NOT decide on a girl's name. It would have been awhile.