Do things sticking to the foot, due to cracking or due to asphalt, affect the validity of ablution and prayer? And is it permissible to use prayer time reminder apps on mobile phones that have copyrights?

What prevents water from reaching the skin must be removed. Slight dirt under the nails or in the cracks of the feet is excused after making an effort to remove it. If it is difficult to remove something stuck to the skin and it is extensive, then one may wipe over it like a splint. As for mobile applications, it is not permissible to copy them if their owners have not given permission.