Question about the public channel filter

I know the filter is 2 posts every 30 seconds, and that holds real true. Ive tested many times that you cant post until the last second ticks.

However I was trying what I sent a message and then 25 seconds later send another message... so now 5 seconds later, i can post 2 more things. Well that seemed to work out... what about 28 seconds? nope, not 28 seconds, it seemed to restart. Since there is no API call to find out the time remaining, and its happening server side, so it doesnt fall under the UI department. Is there some offical documentation on how the timer works? I didnt see the system even mentioned in the live patch notes.

Wasn't sure of the proper forum as it doesnt fall under UI or technical or suggestion :) thanks

edit::

actually,
if i post once, then wait till 25 seconds to post again i cannot post a 3rd time until the 30 second elapses. However, once the 30 seconds are up, I am allowed to post once more, but the 2nd time is not allowed.