Re: Only 3 hours?
Most space launches go to the east, so that the rotation of the Earth contributes to the velocity required to get into orbit. Launching to the west would require a lot more fuel to get to the same altitude.
As to why the different journey times, I would guess it really depends on the timing of the launch:
AIUI the ISS isn't in an equatorial orbit, but is skewed by about 50°, I believe as a compromise to make it easier for Russian launches to reach it. As a consequence of this, and it being in low orbit, the places its path crosses changes from one orbit to the next. Sometimes the station will be in a convenient place when your payload reaches orbit, sometimes you have to manoeuvre and wait for the orbits to sync up.