YANBU.
My DP's sister has just decided to pull a similar stunt on us. Her baby will be 6 months old when our baby is due, and she has booked the christening for exactly 2 weeks after I am due. She told us the date the same time she asked DP to be godparent (and tell him he has to go and be christened first!).
Now, call me unreasonable, but, I am expecting to go overdue, as I did with my first, and I am planning a home birth. I had a c/s the first time, so there is a chance that I may end up being transferred into hospital and end up with another c/s - I could still be in hospital on the day of the christening. I will not agree to be induced, so there is no guarantee that I won't be in labour or just delivered, or whatever around that time.
DP's family aren't particularly happy, as there is only DP, his mum and sister, and then a few aunts/uncles/cousins. It isn't a big family. So everyone expects him to be there.
DP told her to go whistle. He would rather be at home and putting his childs needs above hers. Its not like she didn't know my exact due date - she only booked it 2 weeks ago! If she wanted him to be a godparent so much, then why book it right at a time where it will be full of uncertainty for us!
To be fair, we are intending to go, all being well. But the problem is he can't commit to being a godparent when there is a possibility he won't be able to attend!
And anyway. They are all a bunch of hypocrites. She isn't religious, non of the family is. Her first isn't christened. I'll let you make your own mind up why she is doing it...