Yes dogs aren't that much different to humans at a neurological level. We both have problems gauging time as part of learning. therefore we rely on cues in the environment. You may be surprised but it's likely your sister's dog is attuned to cues like traffic sounds, so the dog anticipates as peak hour traffic sounds escalate that your sister's return is imminent.
Assuming regularity then more specific cues like evening bird calls, delivery vans or her neighbour's car/voice/pet might mean the dog can narrow down fairly accurately when your sister is about to arrive.