The effect on power system of "leading" power factor is that there is more capacitive power. It depends whether you analyse a source (a generator) or a load. If the load has capacitive properties, it can be used to compensate inductive reactive power, however not with such big PF. Usually it is done by inserting capacitors (in parallel or series), and they have very low resistance relatively to their reactance and it is very close to 0.
Considering the generator, by changing its excitation current, it is also possible to make it work as a compensator. There are even special machines designed for compensation work.
Compensating (both by capacitors or compensators) allows to feed inductive loads (like motors) without transmission losses. We don't need to send inductive power to loads.
Answering the question how long: this is a steady state so it does not matter how long PF can be with such value. If load changes or topology of the network will be modified, this PF can change too.
While calculating active power you don't need to know what type of reactive power you take/get. The equation for active power is $$P = Re(S) = |S| \cos \phi $$ where $$\cos \phi = -0.95$$
is your power factor.
In this case, however, the fact that PF is negative means that active power is negative too. When you are considering a load, this means that the load outputs energy to the system, so it works as a generator. If you would consider a generator, the negative active power means it works as a load, so it takes energy from the system. This can happen in fact in one and only state, when the generator's turbine failed and rotation of the rotor is created by rotating magnetic field of the system (the generator works as a motor and it is rotating the turbine).
The apparent power will never be smaller than active neither reactive powers. Because these are complex numbers we can't say which one is larger. The minus sign on your meter means that the power factor, which is calculated as cosine of angle of current phasor related to voltage phasor is in some kind of opposition (so it flows in opposite direction), so the power is.