Is there a way to manually enable time compression during a mission?

Yes, if you enable the cheats.
Type DARKGOAT on the mission select screen. If you've typed it correctly you'll see the word 'outcome' and a number appear next to the mission names.
Then during a mission press SHIFT+A to cycle through the time compression settings.
You can also use the 'skip' cheat instead - SHIFT + S which skips the current mission check forcing the mission to progress to the next phase.

Thanks. I also found out that you can skip ahead in dialogue by opening up the mission briefings display on the command console.

You can also press PageUp to skip dialogue, and go back through previous dialogue, but you don't need cheats enabled to do that.