How long does it take to nurse a mountain horned dragon back to health?

i got 2 mountain horned dragons 2 days ago from a friend..from a friend..ect, they were not kept in good health. they're dark brown, one isn't to mobile but seems like it may a lil better today and is eatin. i bought them moss, an air stone for their water & vitamin powder for their food. how long before i will b able to tell if what im doin is really workin? any info u have on them would also help & b much appreciated..ty