Had he been a Darkfriend for a very long time? Or did he turn just before he went to Tarwin's Gap? After that?

 

 

During my last reread of the Great Hunt the question popped up in my mind and I haven't been able to get it out of my head since

It's certainly never said for sure, but my take on your question would be at least a few years. When he spoke to Rand at Falme he made it sound like he did what they wanted, but they always wanted more from him, things that were worse than the last thing he had to do, etc. I got the impression this progression took longer than the month or so between the battle at Tarwin's Gap and when they started chasing Fain. It seems like something that would take a few years or more.

It seems that way to me too. Some time after he started soldiering, but not too recently

I always got the impression that he had been a DF for years by the time of TGH.

It seems most likely, I was just wandering if any of you experts out there knew better than I did. Thanks for the help, my mind is at ease

There's no definitive answer to this. He was definitely a DF by the time of the DF social in TGH beginning. But as to how much earlier, his conversation/ confession at falme doesn't really give us a strong indication either way. He doesn't refer to anything he did for the Dark, prior to events narrated in TGH. My impression is that it wasn't that long ago, he had too many doubts about his actions. But again, this is not backed by anything in the books.

I would guess Ingtar became a darkfriend sometime before the main series.

Also with the other darkfriends there.