LÖVE

I will be using the physics engine in my next project and thought I'd check: The applyForce method - should that be scaled by dt?
?

I mean, is applyForce the force at any given time, meaning dt is irrelevant, or is applyForce the force per second in which case, dt becomes important?

The force applied by applyForce should not be multiplied by dt in principle. It lasts the duration of dt that you pass to world:update(); if you want it to be applied for longer, you have to apply it multiple times.