Well.. I'd say half an hour.
It's possible, but not recommended. Some of the weaker demons may follow you out self-preservation and the promise of reward, but the more powerful ones..
The animal demons (Hawk, Tiger) tend to be loyal if they get to hunt and fight.
The Shade would probably prefer to simply return to it's cool dim home plane.
The two red demons tend towards Lawful Evil, and will make deals.. that you may later regret.
If you do try that, I'd go with the animal demons.
“She'd become a governess. It was one of the few jobs a known lady could do. And she'd taken to it well. She'd sworn that if she did indeed ever find herself dancing on rooftops with chimney sweeps she'd beat herself to death with her own umbrella.”
― Hogfather