They will be fine until tomorrow. Axolotls are commonly not fed at all for 2-3 days before they are shipped to cut down on waste output and ammonia during shipment, which also takes 2-3 days. Your axies will be perfectly fine, although slightly more hungry tomorrow! Feed them a little extra in the morning. Also, it's probably time to switch to live blackworms at this stage in their development. They are more nutritious, and can be farmed at your home pretty easily if you have time/space. There's a section on this forum about worms in the food forum. Check it out. Cheers!