I dont really understand how to use offset

[Mokona]

Now that I'm getting into 9*+ songs I'm having issues following with my eyes and needing to rely more on my ears. I had originally set the offset to 0.150 which I could set it on the line by following the rhythm of it 90% of the time. However in game I always feel like I'm hearing the note late so I decided to ignore the beat and only push the key the moment my brain registered the final note only which changed it to 0.300 about. I still feel something is off now the song doesnt quite flow right and the long note especially I can tell end early. The thing is I dont really know what method is best since on level 6 and 7 songs I can still reliably get 95% with both methods.

[CCShad]

You've gotta rely on both vision and hearing, and for me at least, it was more about adapting rather than fine tuning the offset. The offset wizard gives a steady, predictable beat, so it can't really account for your ability to play sudden BPM changes or polyrhythms, which you'll see charted out more in the higher difficulties.

The best way to find your optimal offset imo: Go to your in-game settings, display, and enable Early/Late indicators. This will show you more precise information when you hit a note, showing "Early" or "Late" as subtext even on Perfect hits.
Next, choose a song you're comfortable with: It should be a song you know well and remember the tune of, and a difficulty you can play fluently (Maybe 7 or 8 star if you’re getting into 9s and above now?)
Play this song 3 or more times in a row, try to focus on the upcoming beats in your head, and utilize your hearing a bit more than vision. Pay attention to how many Early and Lates you're getting: At the end of each play, on the results screen, it will show how many Lates and how many Earlies you got. If by the 3rd play, you're still getting exceedingly more of one than the other, adjust your offset accordingly.

[dumpworth]

I don't think it matters. I switch between my Bluetooth earbuds, wired headset, and speakers and never had to mess with the offset. The margin to hit great/perfect is lenient. But I would set the music to 50% volume and the hit sound 100% volume if you are having trouble.

[Seth Abercromby]

Offset cannot 'fix' your timing, unless there is a noticeable disconnect between the music and when you need to hit a note to register as a perfect, which seems to at least be the case with the current offset settings you're using. CCShad's advice is solid, but we humans aren't metronomes. I have a tendency towards hitting notes a bit too early, but that has nothing to do with my offset.