If anything, I'd suggest that you be able to re-summon your companion at the end of a short rest.
Mechanically, it seems like the fair thing to do at first glance. There's always been some sort of semi-permanent or at least temporary loss for getting your companion killed in every version of the animal companion ever released. There's a VERY good reason for it:
If you view the companion from an entirely mechanical standpoint, you've essentially just doubled your hit points and put them in a different body. A body you can throw heedlessly into the front lines. Or send straight into a trap to set it off. You have a fearless, suicidal body-guard who will do whatever you want. And if/when he dies? Just bring him back in tip-top shape after you take a nap! No biggy, no psychological trauma or anything... we'll just send him off a cliff this time. That's what summons are for.
But if there's even the slightest hint of loss when you get your best friend killed? All of a sudden, your companion matters. He isn't a suicidal summon anymore. I think 24 hours is just long enough to make people cautious, but doesn't really affect the game. If he dies? You're sad for ONE DAY and all of a sudden your best friend is magically back. You've got to remember that even just mechanically speaking, the companion is a MASSIVE BOON. You're essentially getting a second character! Something has to make people slightly cautious with it, otherwise it’s just a pen-and-paper video game character.
Being able to have birds or snakes or crabs, or whatever else, as companions is fun and interesting. I don't see the point of reducing all these options down to four-footed beasts.
You're right! I love the idea of a ranger with a giant snake companion, super cool- I've played that character before! It's just difficult to make work with the simplified version I cooked up. I don't want the companions to be chosen based on their stats. Be honest, you don't pick a crab because you've always wanted to be “the crab-ranger”... you pick a crab because he has the best AC among animals with a CR of 1/4 and he can grapple stuff. And then you have to FORCE your character to try to make the slightest bit of sense to your DM.
DM: “Why… do you have a giant… crab… friend? Now be honest…”
PC: “I wanted a panther but... well, ya see, he’s an amphibious tank with clamps for hands. 'Nuff said, amiright?”