Requiring derived class to define a method

I am no doubt overlooking something basic but my implementation is obviously flawed. I am trying to require a derived classes to implement a method being called in a base class.

class IClock
{
public:
    virtual void OnTimeExpired() = 0;
}

class Clock : public IClock
{
    ... // ABC not implemented
}

class Application : public Clock
{
    ... // ABC not implemented
}

class DerivedApp : public Application
{
public: 
    virtual void OnTimeExpired() { ... }
}

I rarely use pure ABCs so I thought by not defining the pure virtual method in Clock and Application, it would require all derivatives of Application to define the OnTimeExpired() method. I discovered this will compile and link (MSVS-2017) and if DerivedApp does not implement the method, the Clock object will call an undefined method and crash. 1. Why does this compile without the pure virtual method being implemented? 2. How do I force derived Applications to implement the OnTimeExpired() method?