I'm in a similar situation to yours. I rescued about 15 southern leopard tadpoles from a pond that was just about dried up. Some changed into frogs in a few weeks, and some are taking much longer. I'd say I got them in early to mid-July, and it is now almost the end of August and some only have legs and one or two are still tadpoles. From what I read online, some may take months to change. I did read about some environmental factors that may impact the speed of their changes, such as the number of other tadpoles in the same space, but nothing that I could recommend for you to try.