90% of the time they're the same. If I say an exact time, I'm more likely to say "got back" than "came back." "He got back at 7:30." If there is a chance that someone might not return, you HAVE TO say "came back", not "got back" "100 men marched off to war, and only 5 came back alive." "You came back! I thought you were gone forever!" "After years of sleeping peacefully every night, Bob's nightmares suddenly came back."