How to make a block disappear after time?

If you made a custom block for the ice, you set its tick speed to the number of seconds X 20 you want it to last. Then, in a procedure for when the block ticks, have "place Air at X Y Z."

Or you could have it place frosted_ice (the stuff placed by the Frost Walker enchantment). Frosted ice automatically melts after a few seconds, and even has a cool cracking animation.

The curse of vanishing on Minecraft is one such trouble-maker. When this enchantment is applied on any weapon, it disappears after death and makes it impossible to loot the weapon. This is one of the rare curses and is not easily obtained. The curse is available just in one level and can be found extensively on specific places in the game. As mentioned above, the curse of vanishing was included in the game only in the exploration update.

Here is the full guide to curse of vanishing incase anyone was wondering. When you apply the cruse of vanishing on a tool or weapon, the enchanted weapon disappears after the death of the player. The curse can be applied to almost every weapon on Minecraft.

This is not helpful. The modder want to make the ice disappear, not item disappear.

But yeah, basically use this code for the ice cube on-block-added procedure:

wait [100] ticks thenon server side do

        place [minecraft:air] at x: [x] y: [y] z: [z]

end

To apply the curse to any object, you will need to have, an anvil, the enchantment book and an item you wish to apply the curse on. To perform the curse open the enchantment book. Place the item that you wish to curse and the enchantment book inside the anvil. Now, when you place the item back in the inventory, you can notice that the item has been cursed. When a player dies, the cursed item doesn’t have to be worn to disappear. Even if it is present in the inventory, upon the death of the player, the item automatically disappears. You can use it against your enemy to make sure that he gains no loots after your death. The curse could be both a boon and a bane. It depends on the situation on which the player is and the item that is cursed.  

The inventory trick- 

To use this method to remove the curse, the player must have an inventory. If you don’t have one, then you cannot use this method. You can try the other alternatives instead. This is one of the simple, easy and less time-consuming trick. This trick was also found to work effectively in a few versions. However, if you have an inventory, you can always try this trick to take away the curse. Keep inventory open and go to the game-rule option. Once inside, change the option to True. That is all you need to do. Now, visit again and check if the curse has been removed.