Cannot implicitly convert type ‘int?’ to ‘int’.

Well you’re casting OrdersPerHour to an int?

OrdersPerHour = (int?)dbcommand.ExecuteScalar();

Yet your method signature is int:

static int OrdersPerHour(string User)

The two have to match.

Also a quick suggestion -> Use parameters in your query, something like:

string query = "SELECT COUNT(ControlNumber) FROM Log WHERE DateChanged > ? AND User = ? AND Log.EndStatus in ('Needs Review', 'Check Search', 'Vision Delivery', 'CA Review', '1TSI To Be Delivered')";
OleDbCommand dbcommand = new OleDbCommand(query, conn);
dbcommand.Parameters.Add(curTime.AddHours(-1));
dbcommand.Parameters.Add(User);