My provider is YouTube TV and I have added a shift of 3 hours to the HGTV data since it seems to be East Coast time.
The relevant m3u looks like this:
#EXTINF:-1 channel-id="56401727058813792745219830808424434624" channel-number="9027" tvc-guide-stationid="49788" tvg-shift="+3",HGTV http://adb-tuner.lan:5592/stream/29
But the guide still shows the old times (even after a 'refresh' of the m3u and re-download of the guide)