UPDATE 6.10pm: Here’s the official line from Epic on the return of Daily Challenges under a new name and changed mechanics – namely that they unlock each day and are then replaced en masse every seven days:
“Daily Challenges have been replaced with Limited Time Missions, which are free for all players. By completing objectives, players can earn rewards. As part of the Limited Time Mission, a new objective will unlock daily at 9AM Eastern. Players will have a week to complete these objectives. They will then be replaced by a new set of Limited Time Mission objectives.
“All players now have 70 unique objectives to complete over the course of the season, and can expect free events throughout the season with additional rewards.”
Having just had a look at the challenges, there are a couple of other unmentioned changes here. First, you cannot re-roll the challenges for another (so you’re stuck with those ones which have to completed with friends). Second, these offer a mix of rewards – some XP, some Battle Stars and, this week, one loading screen. If you’re a collector, you’ll want to do at least three challenges to unlock that.