Execution timeout expired in Entity Framework but works fine in SQL Server Management Studio

Question

I am calling a SQL Server stored procedure from Entity Framework like this:

datacontext.INITIAL_CHECK(FileKey);

My connection string has connection time out defined as 600 seconds.

But the stored procedure execution is aborting with an "Execution timeout expired" exception.

When I run the same stored procedure through SQL Server Management Studio, it finishes in 43 seconds.