Unlike weekdays, sat will usually carry very light load in early morning. Also with the new highway, traffic from Taipei is a breeze on sat, but takes "at least" 40 mins. Immigration takes less than 2 mins, but depends on your gate, it could takes up to 10 mins walking from immigration to gate. Keep in mind, cx does close door early if all pax arrived, which is a good thing. If you are the last one walk in the door, even you are on time, expect some evil eyes