It took me some time but I did reach Tier-6. The reason for my late promotion was that I couldn't find that damn bird.
Though I decided to lead a slow life from now on, I didn't want to miss out on the 50x bonus from the promotion mission. There was no info on how it was given.
Should I complete the mission as soon as possible within a time limit?
Would the 50x bonus disappear if I take too much time?
I have no idea. So I decided not to risk it and complete the mission as soon as possible. I can stop levelling quickly once I reach Tier-6. I can upgrade the skill levels first at a normal rate, similar to others, rather than going frenzy while levelling up.
So even though I started to have a slow life, I kept searching for that stupid bird. It was in the third month after the semester started that I was able to find it and kill it.
It was not an easy endeavour.