Divide project at 4 parts. 1 - basement. 2 - base logic. 3- complite designe. 4 - complite full project.
After finished 1 part (8 days / 4 = ~2 days for a part) i will send apk, you will test it, if everything is ok i will send you soursec and you will pay 1/4 of all payment. The same situation with other 3 parts