I always adjust them when I have the heads off.  Tell me about doing it with the belt on.  Manual says LH side crank arrow up is TDC, do #1, then rotate 180, do #3, rotate 180 do #2, rotate 180 do #4.  However, i see people doing it TDC then 90º, then another 90, etc.

I'm assuming it can be done either way?

What’s the 90° in reference to? 

90° on the cam shaft = 180° on the crank. It’s also the interval between TDC when starting at TDC on one cylinder. 

I always do them on the cylinder that’s at TDC on the firing stroke and work my way through the firing order. However, on our other vehicle of another make and model their FSM says to do one cylinder at TDC and the inlet or exhaust of another cylinder at the same time, so only one engine rotation is needed. 

I do prefer the one cylinder at TDC on the firing stroke at a time. 

Cheers 

Bennie

Ok, thats what I was thinking; 180 on the crank is 90 on the cam.  That clears it up for me.