I bet this is what's happening. See the "note" at the end of original post above. When an oil clutch pack disc set sits for a time, they will stick together and won't separate for the FIRST TIME YOU USE THEM. After that 1st "unstick" time,,,your usually good to go.
It is very similar to the effect of taking a glass window pane, and placing a few drops of water or oil on it and placing another pane of glass on top and pressing them together. There is a fancy word for it that I can not recall, but the two pieces of glass will stick together and it would take a bunch of force to rotate or pull them apart.
So back to your question/problem. This is what I believe is happening. Lets break down what you are saying into two parts. Part #1 "Start engine trans in neutral, let run about 20 sec, pull in clutch, wait about 20 sec, clunk as trans goes into first." That is exactly what I would expect to happen. (happens to me also) When you pull in the clutch lever,, the clutch pack is still is revolving "as one" because the pack is not separated yet,,. it is stuck together like the panes of glass. Then when the dogs in the transmission engage, a loud clank is heard. That is the moment when the pack breaks loose.
From this point ON, the pack is broken,,, therefore part#2 makes sense also => Part #2. "Put trans into neutral, let out clutch, wait about 20 sec, pull in clutch, trans will go into first with no clunk. Everytime, hot or cold"
Want to prove if this is what is happening? Try this. When you put your bike away for the night, Tie wrap the clutch lever to the bars. Let it stay overnite with the lever pulled ALL THE WAY TO THE BARS. This should prevent the clutch pack from becoming one and "seting up". When you start it in the morning, STILL WAIT the 20 seconds and foot lever the bike into 1st. My guess is it will be quiet.