I thought that I needed to finalise a specialist hire in order to use them... turns out you don't, but the warning message that is displayed when you try,
You got us - We haven't yet implemented finalizing hires or promotions in the future. You can move another 10 minutes into the future instead - Shame on you guys
...suggested to me that it was a bug that you couldn't rather than it being unnecessary. Hopefully that helps someone else.