The Tikkun is long and you need to finish by Alos. However many try to finish about 30 minutes before alos hashachar to be able to go to the mikvah. That doesnt leave enough time to finish everything. Many people who read the Tikkun and finish in time is because they skip the mishnayos and for good reasons.
1. In the Zohar the mishnayos part is not mentioned it was added much later.
2. To be yotzi limmud hatorah in Torah shebaal Peh one needs to know what the mishna is saying and most people dont know most of those mishnas without reading a perush.
So the good news is that this year I will finish in time IYH because I wont be doing the mishnayos part! I hope this is helpful.