Aikage, I've only used homemade starter cultures and freeze dried Direct Vat Set (DVS) cultures that you sprinkle onto the milk.
I think you are asking about Prepared Culture or Mother Culture style starter cultures and suspect your directions mean maintain at 76F. I know fellow member Tea in Queensland uses this system so I'm hoping she can answer.
Assuming your house is colder that 76F, options to keeping warmer are a small "health" heat blanket, placing on top-back of fridge, placing in oven and leaving light on similar to making yogurt ( i suspect you'd need to keep the door open otherwise it will probably get warmer than 76F).
Hope helps, John.