Yup, the event reward definitely needs a cooldown timer.
Though until then, a suggestion: start an 800-rep NR or Omega project, or a 20-hour doff assignment, right after receiving your shard. Then, whenever that project or assignment is complete, you know you're eligible for your next shard.
I logged on to the message forum this morning just hoping to see a thread on this very subject. It would definitely be nice to have a visible cooldown timer somewhere for this event and others like it.
It's a pain in the butt that there's no visible indicator of the cooldown.
I think a simple way to achieve this would be to get a "buff" of some sort when you receive a shard, so there's a marker on your captain that counts down. The idea would be the same as the XP boost you get during Q events, or the CXP boost during the Junior Officer Appreciation events. It wouldn't need to actually do anything, just last for 20 hours.
Just add a daily mission, so we won't need tracking it by anything outside of the game. That'll definitely help people know it's time to get a shard.
On the other hand, dailies mission are wonky and not actually dailies. They use random algorithm, which makes me wonder why they're called dailies in the first place. That's an altogether separate issue though.
STO is the BEST game ever and the players absolutely LOVE it.