Whisper recipient limit - what does "per day" mean, exactly?

I’m working on converting a bot to send whispers via the new API and in the documentation it says that there is a limit of 40 unique recipients “per day.” It doesn’t say how this is handled, and I don’t want to make the wrong assumptions. I can see three reasonable interpretations of this:

  1. It uses the same system the IRC rate limits, where the first sent whisper triggers the start of a 24-hour period. This seems most likely, but then this an API call and not IRC, and APIs handle rates differently.
  2. It works like the bucket system the APIs use where it refills over time, and each recipient locks out one of the 40 slots for 24 hours each whisper. The headers on the whisper response show the normal bucket data, so if it works like this I don’t know how to tell how many users are left.
  3. There some arbitrary 24-hour period that defines the day, like all limits are reset at midnight UTC or something like that.

Is this spelled out somewhere in the documentation and I just missed it? If not, is there any way to get some clarity on exactly how this is handled?

I believe it’s (1) as the Whisper API feeds into the same system that /w did.

Wow that was fast! I will move forward with that first interpretation then. Thanks!