In Germany during the 18th century (esp. early 18th century), how soon after birth would baptism commonly take place? Of course it wasn't the same for every child, but was there some sort of usual time frame to be christened? Was there a specified time frame by the Church or by the government for the parents to baptize their child? I am asking specifically about the Roman Catholic Church.
I know that this is a request specifically for the Catholic Church, however, I can give you examples from grandfather's ancestors. He was born Lower Saxony, so he was a Lutheran.
Example 1: B. 5 Sep 1779 Bap. 10 Sep 1778 Example 2: B. 24 Apr 1782 Bap. 28 Apr 1782
I have not seen any evidence that the government would set deadlines for baptism. All of the church records I have seen were maintained by the church. The civil registers I have seen from Cologne, Germany (a predominantly Catholic area) did not ask if the child had or had not been baptized when the birth was registered. Any deadlines, if they existed would have been from the church. I agree with the second post. Parents would baptize their children as soon as possible because of the high rate of mortality for children.
Wikipedia states that many children of the 17th and 18th century were baptized on the day they were born and give 3 examples. Also, see this article from Brigham Young University for more info on baptisms in Germany
It is a pdf file you can download and discusses genealogical research in Germany.
Hope this helps.