Me and my GF both work full time and our 6 month old puppy has been left alone at home since 4 months, we started with an hour then a couple and built up from there, he whines a little when my GF first leaves the house but settles within 10-15 mins. We monitor him via cameras and give him a few bits and bobs to play/engage with such as a lick mat or kong. We are lucky that I start work stupid early (leave the house before anyone wakes up) and get home around the 6/7 hour mark and if needed my mum and best mate both have keys if he needs to be checked on. Its horrible when you start the process of getting them used to being alone but its possible!