Approximate time it takes to go from Army basic training to becoming a Special Forces soldier?

Yes, this sounds like a complete fraud. As others have said, through the 18X program you could be done with Special Forces training within 2 years of enlisting, although it's a 5 year contract. This would have given him 1 year on a team, at which time he most certainly would NOT have been traveling the world "basically as an assassin." First, that's not what Special Forces do. Second, as a first year Special Forces Soldier, he would have been doing similar things to what a lot of first year Army NCOs do. Based on what you said, the guy is a complete fraud, though he could have served in some other MOS and be making up stuff about Special Forces.

Y'all are forgetting though that if you go the SEAL-to-Ranger route, with a stop-off in Marine Force Recon Sniper School, you can become a Green SEAL Ranger Beret Recon Scout SF Sniper in only 6 months, giving this badass 2.5 years to travel the world and be basically an assassin.