Jelena,
if you have a baptism or burial record I think you should put in the exact date of the record. It tells me, the reader that you a record to back up that date and there is no estimation or guessing.
The question then is what status indicator should you use: About/Before/Exact?
Many people use before because they were obviously born before they were baptized - this is my least favorite. Before is too big and too imprecise; it could mean days before, weeks before, months before, or years before.
About is much closer to the truth, as in the vast majority of the time (it was required by law) an infant was baptized soon after birth (yes, I know you can all give me examples of someone being baptized years after birth, don't bother, that was the exception, not the rule).
I actually prefer exact in time periods (16th and 17th century) when there is no possible way to ever know the true birth date and the baptism date is a de facto birth date. The date is precise from the record and can never be improved. In the biography, I always note the date is in fact a baptism (or burial), and of course include the source.