In a day or less you should start to see active fermentation. The airlock will bubble but you wont always see high krausen, the billowing clumps of foam that form during regular fermentation with a full batch. Whats important is that you will start to see an ever increasing deposit of yeast at the bottom of the jug. By brew day you should have a thick layer of eager yeast, ready to give your beer a head start. Make sure to get it all into your wort.
Using a yeast starter like this will produce fermentation in less than a day, sometimes even hours after adding. Good luck and happy brewing!

