There’s a total tally per 24 hour period and this cycles exactly to the time that the like was previously used.
For regulars (and new folks too, I think?) it used to be 50 likes, but I complained about it here and our friendly admins decided to give us a bit of extra after a discussion:
So in any given 24 hour period starting at any point during the day, you have 75 likes. If you used them all within 1 hr, you will have to wait for 24 hrs from the time you used the first one to get 1 back, but within the next hour, you would have all 75 back.
But if you used 15 every hour for 5 hours, you would get 15 back during the first hour, and another 15 from then on until 24 hours from the time you clicked the last one about 5 hours later.
Imagine each like being an individual entity instead of all of them in a package…
Actually, think about each one as being a boomerang, every time it leaves your hand, it returns eventually, and that time in between, you cannot possibly throw it again. Now say that boomerang leaves your hand and returns 24 hours later, on the dot. And you have 75 at your disposal…
We have no specific counter to actually know how many we have left, as far as I can see. It would not really serve much purpose… Would you start rationing your likes if you were running low? I would still try to like a post that I would have otherwise liked anyway.
Hope that helps a little bit… Sorry about the poor analogy, it was the first thing that popped into my head…