This is very simple, however that's not always a good thing. In the skript you used command cooldown, which is not a good for this purpose. Here's a couple reasons why:

-Whenever the skript reloads, all command cooldowns for all players resets. This means on server restarts or whenever reloading the skript, players can skip the cooldown and get their daily reward early.

-Additionally, skript cooldowns run on TPS, not time/date. This means if your server does not constantly have 20 TPS, players will need to wait more than 24 hours for their daily reward.

Now these are not horrible issues but they definitely need solving. You can solve this issue by using skript's date and time feature. You can get the current date with %now%, and you can compare difference in dates with time spans. This fully solves both problems stated above. If you need any help, contact me on discord: quallysus