You can believe in my assumption if you agree with that laddering is a proxy for practice and if one account corresponds to one person.
So as of this moment the average top 100 GM player in:
Korea has played ~319 games
EU has played ~197 games
AM has played ~178 games
The average starcraft game is said to be around 20 minutes so those games translates into:
319 games ~ 106 hours
197 games ~ 66 hours
178 games ~ 59 hours
Since Season Twelve started on March 12, 16 days has passed. A daily average is then easily calculated.
106 hours ~ 6,65 hours ~ 6 hours and 30 something minutes per day.
66 hours ~ 4,14 hours ~ 4 hours and around 15 minutes per day.
59 hours ~ 3,71 hours ~ 3 hours and 40 plus minutes per day.
Foreigners should practice more! Although the comparison might me off since there are more actual pro gamers in Korea. Another note to think about is the Korean vs foreigner skill gap and how much less it could be if foreigners practiced more.