Understanding AVAudioTime in AVAudioNodeTapBlock? Is there a way to get time relative to a scheduled Buffer?

I'm using AVAudioEngine to play AVAudioPCMBuffers. I'd like to synchronize some events with the playback. For example if the audio's frame position is >= some point && less than some point trigger some code.

So I'm looking at - (void)installTapOnBus:(AVAudioNodeBus)bus bufferSize:(AVAudioFrameCount)bufferSize format:(AVAudioFormat * __nullable)format block:(AVAudioNodeTapBlock)tapBlock;

Now I have frame positions calculated (predetermined before audio is scheduled I already made all necessary computations) . So I just need to fire code at certain points during playback:

[playerNode installTapOnBus:bus
                          bufferSize:bufferSize
                              format:format
                               block:^(AVAudioPCMBuffer * _Nonnull buffer, AVAudioTime * _Nonnull when) { 
      
         //Inspect current audio here and fire...
}];

 [playerNode scheduleBuffer:fullbuffer
                        atTime:startTime
                       options:0
        completionCallbackType:AVAudioPlayerNodeCompletionDataPlayedBack
             completionHandler:^(AVAudioPlayerNodeCompletionCallbackType callbackType) 
     {
          // some code is here, not important to this question.
    }];

The problem I'm having is figuring out at what point in full buffer I'm at within the tap block. The tap block passes chunks (not the full audio buffer). I tried using the when parameter of the block to calculate the frame position relative to the entire audio but have be unsuccessful so far. I'm assuming the when parameter is relative to the buffer passed in the tap block (not my entire audio buffer I scheduled).

Not installing a tap and just using a timer before scheduling my fullBuffer has given me good results but I'd rather avoid using a timer if possible and use sample time.