My group did 1200m of ExT on Friday morning. This was due to our facility being unavailable in the afternoon. It was a quick and relatively easy session for all of them. They could have easily returned in the afternoon and repeated the same session, though I’m sure they would have thought that I was nuts.
By contrast they did 2200m of ExT on Wednesday afternoon at our normal practice time and found the session to be challenging. Same target times, same recoveries and more awake.
From experience I view ExT in the 1000-1500m range to best viewed as a form of recovery for even moderately talented + fit athletes. Sessions 2000m+ are for increasing aerobic capacity or power, even for reasonably accomplished athletes. Just my 2 cents.