The NBT library included in MCPE can load TAG_Long values fine, but when saving, only 32 bits are saved, because the save method is declared as

CompoundTag::putLong(std::string const&, long)

when it should be declared as

CompoundTag::putLong(std::string const&, long long)

On ARM, long is a 32-bit integer, and long long is the 64 bit integer.

This affects world time and world seed, since as far as I know those values are the only values stored as longs.