Anomalies with the now() function

I have a trigger set up on a db - when a row is added to a certain table (say Table A) in my db the trigger calls a function and then the function enters another line in a related table (say Table B). Here's the problem, the first addition to Table A may show the time of the addition as, for example 19:01:53. This is correct. The second addition, triggered by the first additon, shows a time of say 19:01:10! The addition of the row to Table B uses the now() function to determine the time the new row is added to the table. This should in theory match the time (to within a few milliseconds at least) the first row was added, since the trigger is immediate. However, I am seeing major time differences? How reliable is now() - has anyone seen anything similar ?

Reagards,
Kevin Byrne