Pearl city express is Super Fast Express, so you can count on it for reaching on time.
You need to get down at Madurai, have snacks near Railway Station and from there, go to Arappalayam Bus Stand. Bus will leave from there at 6. 10 Am. It will not be crowded much, so you can have relaxed travel.
They will stop for breakfast in a small hotel at Tamilnadu/Kerala border. The food was nice there. You can have good breakfast at cheap price. Then head onto the mountain.
The bus will go through steep hair pin bends will stirrup Adrenaline in your body for sure. If you want to have more adventurous mountain ride, go in bus. You wont get this experience in Car.
Then, Finally you will reach Munnar around 11. 30 am.
While return we took the other path to Reach Ernakulam. We boarded Kerala SRTC bus from Munnar around 6. 30 Am and reached Ernakulam around 1 Pm.
Usually, while coming down from hill areas, some will feel vomiting sensation. So it is better to book NON A/C car downhill as you wont feel suffocated and you will be comfortable.
Overall, the journey was a good experience.