I know it takes about 26 days for a sylesti to become an adult but if a user uses two magical pies on one pet does it take away double the amount or does the second pie not work?

Each pie adds 144 hours (6 days) to the pet's maturity. There is a cool down period of 72 hours (3 days) after you use a pie.

So you can use multiple pies, with each pie adding the same amount, just that you can't use them at the same time. You can only use pies on adolescents, so I think it's a max of 2 pies, and your pet should be an adult before you can use a third.

Note that pies add to maturity, which you can't see from the pet profile so it can seem a little confusing. The pet's age in the profile notes the duration since the pet has been created (pie does not affect that). What the pie affects is the maturity, which can be seen in the image url if the pet is genetically tested. At the end of the url, there's a &maturity=___, where the number there denotes the pet's maturity in hours.

okay thank you!

You're welcome =)