I don’t recall TR coaches talking about it on the podcast. Time to exhaustion as a metric was introduced 5+ years ago (IIRC) in WKO and is discussed here:
Coach Tim Cusick wrote that article, with input from Dr Coggan.
There is a good webinar on YouTube - “Building FTP, TTE and Stamina with WKO5” that talks about it. Without listening to the podcast again, the slide on page 20 (download link from YouTube webinar) describes what Brennus wrote:
on the slide it notes pushing TTE out by doing longer upper tempo and lower threshold intervals of 85-94% of FTP. I stumbled on this method of increasing TTE four years ago, after watching a GCN video. It took my TTE (by definition at FTP) out to about 65-70 minutes, as actually field tested outside.
Go visit the Sweet Spot Progression thread to read about others achieving long TTE (at FTP) and stamina / high fatigue resistance (long efforts under ftp). This approach will build metabolic fitness, and you’ll reach a point of diminishing returns (FTP at high % vo2max) when its time to raise the roof and work on vo2max. But working on vo2max is about increasing cardio fitness. Working on TTE is about increasing metabolic fitness.