You can compete in a DT 12 times a day and ELO
4 times a month. If you miss one, you have an identical chance (for an identical reward) soon after. These missions are five per fortnight, but if you miss one, a DIFFERENT set replaces them. It's five different missions a fortnight.
Think of it the Lds. If you miss an Ld, you miss it. "Why complain you'll get another chance next week?" That's for a different Ld. Now, these missions are more difficult than the most current Lds, but are less rewarding.
Combining the time limit to obtain the cards (clintz or credits?) and unlock the missions, the rask being listed on the mission page (achievements + OCD!), and the original timing of this concepts release (no picking clans in packs
-this problem was fixed) and you should be able to see why people aren't too fond of this.
Now, the main (and, as far as I can tell, the only reasonable) complaint is the time limit. If the staff increase the time available that should end all complaints, especially as the newness value is wearing off and the cards are becoming more reasonably priced.