The Bug:

Mundane, thick, and awkward splash potions don't give axolotls 1.5 minutes of moisture.

Steps to Reproduce:

• Obtain a mundane, thick, and awkward splash potion.
• Set the weather to clear.
• Summon an axolotl outside of water.
• Inspect its Air NBT value through the use of the following command:

/data get entity @e[type=minecraft:axolotl,limit=1,sort=nearest] Air

• Take note of this value.
• Splash the axolotl with either a mundane, thick, or awkward splash potion.
• Inspect its Air NBT value once again.

/data get entity @e[type=minecraft:axolotl,limit=1,sort=nearest] Air

→  Notice how the Air value did not increase from what it previously was, despite splashing the axolotl with either a mundane, thick, or awkward splash potion.

Information:

Most likely intended based on the resolution of MC-106812.