KöMaL 2017 K540

On the planet XL, there are 180 days in a year, and 10 days in a month. Every seventh year is made an XL year, which means adding an extra day to the third month, making it 11 days long. The week consists of 5 days, called AX, EX, IX, OX and UX, in this order. Pax was born on the first day of the fourth month of an XL year. Today, on an OX day, he is exactly 25 years old. His son, Felix is 2 years, 3 months and 5 days old today. When Felix is exactly half as many days old as his father, he will have his coming of age ceremony. On what day of the week will the ceremony be held?