I want slow down my project's playback at measure 36, the last measure before the end.
 
So I go to the Tempo view and insert the tempo change (from 72 BPM to 68 BPM). I can see on the tempo map that I have done this correctly. Prior to measure 36 the tempo is 72, and at measure 36 the tempo line drops to show a tempo of 68. Also, I can see in the Tempo List that I have done this correctly. There's a tempo of 72 at measure 1, and a tempo of 68 at measure 36.
 
But when I go back to the track view and hit play, the entire project plays back at 68.
 
Suggestions?

How are you detecting that the tempo is 68 before measure 36? If you record the metronome to an Aux track before making the change at measure 36 does the initial tempo go out of sync with that audio?

This may be a dumb observation, but if you change tempo with already recorded audio, the audio will not change at all ... it will still play the same. 

Well today it's working. Or maybe I was so bleary-eyed last night that I didn't know what I was doing.
 
Thanks for your input.