Update UI on main thread from AFHTTPRequestOperation - ios

Question

I've built a Rails backend for an iOS app that lets users access a RESTful API only after having authorized the device. Basically authorization is managed by retrieving a token.
When the user submits username and password, the webservice gets called with an AFHTTPRequestOperation (see code below). I also display to the user a HUD (MBProgressHUD) to track the progress of the request. I've set up callbacks for success and failure and I want to update the HUD and let it stick onscreen with an updated message for a couple of seconds before dismissing it.
//Set HUD
MBProgressHUD *hud = [MBProgressHUD showHUDAddedTo:self.view animated:YES];
hud.mode = MBProgressHUDModeIndeterminate;
hud.labelText = #"Authenticating";
//Set HTTP Client and request
NSURL *url = [NSURL URLWithString:#"http://localhost:3000"];
AFHTTPClient *httpClient = [[AFHTTPClient alloc] initWithBaseURL:url];
[httpClient setParameterEncoding:AFFormURLParameterEncoding]; //setting x-www-form-urlencoded
NSMutableURLRequest *request = [httpClient requestWithMethod:#"POST" path:#"/api/v1/tokens.json" parameters:#{#"password":_passwordField.text, #"email":_emailField.text}];
//Set operation
AFHTTPRequestOperation *operation = [[AFHTTPRequestOperation alloc] initWithRequest:request];
//Success and failure blocks
[operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject){
NSError *error;
NSDictionary* jsonFromData = (NSDictionary*)[NSJSONSerialization JSONObjectWithData:responseObject options:NSJSONReadingMutableContainers error:&error];
NSLog(#"%#", jsonFromData);
_statusLabel.text = #"Device authenticated!";
hud.customView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:#"37x-Checkmark.png"]];
hud.mode = MBProgressHUDModeCustomView;
hud.labelText = #"Authenticated!";
sleep(2);
[MBProgressHUD hideAllHUDsForView:self.view animated:YES];
}
failure:^(AFHTTPRequestOperation *operation, NSError *error){
NSLog(#"Error");
sleep(2);
_statusLabel.text = #"Wrong username or password!";
[MBProgressHUD hideAllHUDsForView:self.view animated:YES];
}];
When the success / failure operation callbacks get called:
I try to update the HUD mode and text;
I wait sleep() for a couple of seconds;
I dismiss the HUD [MBProgressHUD hideAllHUDsForView:self.view animated:YES];;
I've also tried using dispatch_queue_t dispatch_get_main_queue(void); and run the HUD update on the main thread but to no avail.
Any ideas on what am I getting wrong?