I had a molly give me 18 babies, and of those, only 2 survived to reach an inch. The water parameters in their tank were perfect and stuff, but only have 2. It has been about 1 1/2 months, and they are a little more than an inch. Guppies seem to get bigger. I put my fry in another tank with the water params the same as their birth tank. Still I had 40+ guppies in my last batch, and have only about 7 of them left. A lot depends on the breeding, if they are inbred or not. In a 10 gallon tank, my other babies grow out much quicker. I do water changes at least every other day and do about 20%. I feed them 3 times a day. Just remember that no matter how many babies you get, a lot of them can die before they mature.
Also, I had my guppies and mollies in the same 29 gallon tank. They simply wouldn't pop. After moving guppies to their own 12 gallon tank, I quickly got guppy babies. They do produce faster. Good luck