Get a segment of audio from a blob in javascript

I've used this recorder example which records audio and then encodes it into a blob of type "audio/wav" (which can be played by HTML5 audio elements).

If I want to retrieve only the first 5 seconds of this audio as a blob, I presume Blob.slice(start, end) could be used, but I don't know what to specify as the start and end indexes.

The audio sample rate is 44100Hz.