Lately i like to do mine as i approach low brace, when the bulk of wood removal is done.  But that's just me and my way 

To verify what Chris said, i did a really deep heat temper on a hickory pyramid stave and it gained an insane amount of weight.  I removed all the "toasted" wood and then some and it was still VERY tempered.  I suspect the tempering was still evident after i'd removed half the thickness.