Is force applied over time? I am confused on what force is as a whole.
I understand a force is a push or pull, but is this push or pull over a certain time interval? If not, how could a force be applied if there is no time interval?
To be more specific, when a force is in an equation (say for example the equation of work W=(F)(d)), does F mean average force or instantaneous force?
 A: It might be more correct to say that a force is a pushing or a pulling. It is meaningful to talk about how big a force is at a particular instant: it's how hard am I being pushed or pulled on right now? Think about slowly compressing a spring. The spring pushes back with a certain amount of force that increases the more you compress it. We define a variable (force) to describe how much it's pushing back at any particular moment, not just how much it pushed back on average over a period of time.
All measurable forces last for a nonzero amount of time. The whole event of getting pushed by an impact or pulled by something you're holding on to isn't a force at all, but an impulse, which is what your intuition is reaching for when you're trying to think of what the mathematics of "a push or a pull" should be like.
The equation $W=Fd$ is a special case of a more general equation that requires more complicated math. It holds only if force is constant across the displacement $d$. Therefore the force at any given moment across that distance must be the same as the time-averaged force, and the distance-averaged force.
A: From page 160 of Physics for Realists, a force is the ability of one body to change the impetus (momentum) of another. With this definition, there doesn’t really have to be a time interval specified. The same amount of force could be applied for 2 seconds, 10 seconds, or even indefinitely. Time doesn’t affect the amount of force, but it does affect the amount of change the force has done over time.
With the formula for work, this is the force applied over a distance. So the force is being done constantly throughout that distance.
A: 
Is force applied over time?

$$F= ma = m\frac{dv}{dt} =m \frac{d^2x}{dt^2 }$$
Acceleration requires a change in velocity over time and velocity requires a change in position over time. So a force is the result of a change applied over time. In a static system where the sum of forces is equal to zero, the time a force is applied is irrelevant. For work done, the time required for the force to move an object a given distance is also irrelevant. In dynamics, a force applied for a given length of time is called an impulse.
A: When force appears in an equation, such as the equation for work, it typically refers to the average force over a certain time interval, as this is a more practical concept in many real-world situations. However, in some cases, such as when studying the motion of objects at very high speeds or when analyzing the behavior of objects at very small scales, it is necessary to consider the instantaneous force.
In general, it is important to keep in mind that the concept of force and its application in equations can depend on the context and the level of detail required for a particular problem.
To your second question, force depends on time if it varies with time. If it is constant, then the duration over which the force is applied is sufficient.
