A well tested career assignment station started experiencing 1 min+ delays between placement of job site block and villager transformation. 

The station holds the villager in place while the player destroys and replaces a job site block to select the desired trades. 

An unassigned job-site block was discovered13 blocks away (12 blocks in one direction and 1 block over) and when removed the the career assignment delay was eliminated.

It appears the villager had trouble resolving which job-site block to associate with causing significant delays. 

Note: while I have resolved my issue, there does appear to be a bug to be fixed.