I cant tell you what the code says or doesnt say, I doubt it tells you but I can tell you how I was taught and how we instructed our electricians (but they did it as they pleased anyway lol)
Hold the stripped ends together close and in paralell (NOT pre twisted) and twist the nut till she bottoms out and stops turning then give it a few more twists so the insulated covered portions turn a couple times around each other which gives the twisted pair more strength versus the nut alone having to do all the holding.
As I recall (long time no warranty) thats the way the wire nut manufacturers recommend although Ive seen it done both ways and sure either will work BUT UN TWISTED WAS OUR METHOD.
This may be like asking which brand of oil or sparks plugs are best, with different methods and opinions so I gave ya mine......
PS this was for single solid wire, if its stranded I usually pre twisted,,,,,,,if one wire is stranded the other solid, I had the stranded one a bit longer then the solid one