For baptism, it is, 'an even broader time field'. It could be months or even years. Certainly as long as the gap between when the religious leader deems it suitable to hold a public ceremony. That gap would be as big as possible to ensure the more lucrative private ceremonies happen. Even in those 'priest' fearing times it was not uncommon for some families to wait years before they formally named their children often enmass when someone is getting married so they do a job lot.. The only thing you can be sure of is that the child was born before it's baptism. About implies he could have been born after as well ;-) .A sort of preemptive baptism I guess. I think before indicates the date is a baptism rather than a birth its the only way to do it in the profile. Burials don't have this problem in such big way.
I wonder at times why the automatic biography is there in the first place it is often completely different from the final biography where a date has been found later, the profile is altered and people forget it's there. That goes for incorrect parents links as well.. Perhaps an ability to indicate its a naming ceremony rather than a birth would be good. A full naming ceremony date is really needed before 1837 in the UK as it really aids searches but it does not imply an accurate birth date only exact does that. A naming ceremony or registration is after all probably the first written document that can or will ever be located. Before or after is a one side range, About both sides.