Попробуйте, readStream - это ваш CFReadStreamRef:
#define _kCFStreamPropertyReadTimeout CFSTR("_kCFStreamPropertyReadTimeout")
double to = 15; // 15s timeout
CFNumberRef num = CFNumberCreate(kCFAllocatorDefault, kCFNumberDoubleType, &to);
CFReadStreamSetProperty(readStream, _kCFStreamPropertyReadTimeout, num);
CFRelease(num);
Константа для времени ожидания записи: _kCFStreamPropertyWriteTimeout