Ok, so I'm planning to make a feat that gives a player two separate abilities. However, once you've used one of them you cannot use either of them for the rest of day.

Question of the day is: how do I make a feat with two abilities that have one "use slot?"

With difficulty. 

The way that is accomplished for stuff like class features is to create the feature, then attach an Action to that feature with “Limited Use” data mapped to it to cover the total number of uses for everything. Then, you would attach “Optoons” to that same class feature and those would get the various actions attacked to them. That way everything would nest together. (Like how Superiority Dice and Maneuvers were done for the Battlemaster.)

But Feats don’t have fully programmed actions for options. So the best you’re likely gonna do is make 1 Action with the limited uses data attached, And then create the two abilities each as their own action without any limited use data. (As they are all attached to the same feat it should still keep things attached the same way, so you should be fine.)

Whenever the player clicks/taps either of the individual abilities. The sidebar that automatically slides out (with the full descriptions) should still link to that first Action and the limited use boxes should be accessible.

Yooo, thanks for the help. I've had quite a headache trying to figure it out on my own.

As usual, happy to help.