HLS Latency Broadcaster is the delay between live and the user give or take. No comparing stream start it’s just the timestamp difference between the timestamp in the chunk and the current local time, I believe.
In addition, so be careful:
https://www.twitch.tv/p/en-gb/legal/developer-agreement/
3. Limitations. You must comply with all instructions and requirements in any integration documents, guidelines, policies, or other documentation that we provide or make available to you. You will not reverse engineer, disassemble or decompile the Program Materials or otherwise compromises Twitch’s rights in the Program Materials