With the quest Liberation of Skyrim I'm up to 'Liberate Falkreath Hold' but Galmar will NOT show up where he's supposed to be no matter what I do! I did the player.placeatme command for him, but he just walked away and didn't
offer any dialogue associated with the particular quest.

I also tried fast-travelling back to the camp and waiting 24hrs; Still nothing. I did change the timescale from 20 to 10 before this quest. So do you think that this had anything to do with it? Should I just wait 30 days while doing other quests and come back?

This command shouldn't be used for named NPCs since it creates a copy of the original character which usually can't be interacted with.

The moveto player command should be used to bring NPCs to your location.

Suggest you reload a save before cloning Galmar and try again. You could also try the setstage console command listed in the Bugs section http://www.uesp.net/wiki/Skyrim:Liberation_of_Skyrim