<p>I printed a lot of models in last month. I spent 2 kg filament in total. I want to know how many hours have been passed while printing. As far as I read, 1 kg PLA (1.75 mm) is about 110 meters long. My default print speed is 70 mm/s. The nozzle diameter is 0.4 mm. The nozzle multiplier in the simplify3d is 0.9 .</p>
<p>In a very basic math,
220÷(0.7×0.04÷0.0175×0.9)=~ 153 hours.</p>
<p>Is this correct?</p>

Your math looks correct, and is also a good approximation for what I've seen in the first few weeks with my own Ender 3.
Another way to calculate (to check yourself) is to calculate the volume extruded (nozzle area times extrusion percentage times print speed -- be sure you convert everything to the same units!) in a given second, multiply by the density of your filament (common PLA runs about 1.2 g/cm^3), and get a rough figure for how long it takes to print a kilogram of filament.  Your actual print time will always be higher than this approximation, because there are moves during which the extruder isn't running, infill is often set to lower extrusion level, and of course there's setup and cleanup time to account for.