gistfile1.cs

private struct Row
        {
            public int UserId;
            public DateTime DateUtc;
        }

List<Row> table = new List<Row>
            {
                new Row { UserId = 1, DateUtc = DateTime.Parse("2012-01-05 17:00:00.000") },
                new Row { UserId = 1, DateUtc = DateTime.Parse("2012-01-26 17:00:00.000") }
            };

            var total = 0;
            foreach (var row in table)
            {
                var row1 = row;
                foreach (var otherRow in table.Where(r => r.UserId == row1.UserId))
                {
                    if (row.DateUtc.Year == otherRow.DateUtc.Year && row.DateUtc.Day == otherRow.DateUtc.Day && Math.Abs(row.DateUtc.Minute - otherRow.DateUtc.Minute) >= 60)
                    {
                        total++;
                    }

                    if (row.DateUtc.Year == otherRow.DateUtc.Year && row.DateUtc.Day != otherRow.DateUtc.Day)
                    {
                        total++;
                    }
                }
            }