It's been so hot the dogs lay down in the bare floor instead of on their beds. I have shows coming soon and they all have ugly calluses that I can spot from a mile away. These are not old calluses, more like red hairless spots for now.
I'm going to get Corona ointment, but for the shows I know people use chalk to cover them.
Can you recommend me an specific product?
Any input appreciated.

Try Bag Balm right away. It's made for sore cow teats or was originally. It works for my dogs. It's sold in pet supply stores and in some drug stores. Cost is about $10 and it's in a good size, green tin. It lasts even with 10 dogs.

Apply it heavily overnight, best time to put on alot. Then use a smaller amount 3 times during the day. I put a thin, older bed-sheet down so it doesn't get too sticky on my bamboo wood floors at night. The sheet is comfortable & cool for the dogs. I refold it for the next night the opposite way and wash it the 3rd day.

The dogs lick off whatever you put on them. What is the point?

Not all do. Most of mine don't. If they do, try saran wrap or something around it for a couple of hours.

If the OP does nothing, the dogs calluses will continue to enlarge.

Bag Balm is good stuff for animals and people.

I use it on my heels, in the summer with sandals on all the time it works really well at night.

SO WHAT IF A LAB HAS CALLUSES!!!!! Once there you live with them. I bet not one has ever been fixed!

Well then I'd bet you would be wrong. If left unattended calluses can become rather large and start to crack which could lead to infection. Some years ago I had a dog returned to me with the most dreadful calluses. I applied Bag Balm several times a day, massaging it well. The calluses were greatly reduced and cracks were healed. Yes, they do lick a lot off but if you take a few minutes to massage it in you will have good results.