They are in Records of Eminence Active Quests. That Challenege Accepted alert that appears above your character like Level Up does indicates you have one active. They are added to the active ones automatically if you are logged in during the 3 specific time periods (2 hours each) during the day. One of the recent dev notes says the schedule. The first time you complete it during the time period (or afterward before a new one starts), results in a Copper AMAN Voucher. Two of those can be exchanged for one Pluton.

http://www.bg-wiki.com/bg/Records_of_Eminence

Times Sunday Monday Tuesday Wednesday Thursday Friday Saturday
5:00 a.m. - 7:00 a.m. (JST)
8:00 p.m. - 10:00 p.m. (GMT) Vanquish plantoids Vanquish lizards Vanquish vermin Receive seals Gain experience Vanquish aquans Vanquish beasts
12:00 p.m. - 2:00 p.m. (JST)
3:00 a.m. - 5:00 a.m. (GMT) Vanquish vermin Receive seals Gain experience Vanquish aquans Vanquish beasts Vanquish plantoids Vanquish lizards
8:00 p.m. - 10:00 p.m. (JST)
11:00 a.m. - 1:00 p.m. (GMT) Gain experience Vanquish aquans Vanquish beasts Vanquish plantoids Vanquish lizards Vanquish vermin Receive seals