Delay Potion( Complete Mage, p. 41)
You can drink a potion and postpone its effects.
Knowledge (arcana) 1 ranks,
You can drink a potion and delay its effects for a number of hours equal to your Constitution modifier (minimum 1 hour). At any time during this period, you can activate the potion's effect as a swift action. If the duration expires before you activate the potion, it is wasted. You can delay only one potion at a time. You must activate a delayed potion before you can choose to delay another one.