Amount of time you can leave a new dog & how long for play time?

Our puppy has just turned 12 weeks old and providing he has been exercised and been to the toilet he can be left for 3 hours with no issue. He loves it in his crate, has lots of toys and we give him toys he has to work to get food from. He loves the Kong / Sumo, and the Kong Quest

For how long to play with him, it depends what sort of play you are doing and how quickly your pup tires. When I play with our puppy I tend to play hard with him (tug of war, chase etc) and mix very short training sessions in with our play. Usually after 30 - 45 minutes of that he's ready to go into his crate for a nap. However when Rey plays with my bf it's much slower and doesn't involve as much training, so he can last a few hours before he needs a nap then.

As well as play sessions Raiden gets walks too. We're usually out for an hour, but at least half of that is him being carried so he doesn't over-exert himself. He does get to walk on lead and run off lead too though

Usually our day is broken up into small chunks of play (ranging from 30 mins - 1.5 hours) with a few hours napping in between. Over and over. His biggest nap usually comes after his walk, when he'll sleep for 2 - 3 hours straight. As he gets older he'll have more time up and doing things...currently he gets excited and tired very quickly, so nothing lasts very long

As another book recommendation I really like The Happy Puppy Handbook, by Pippa Mattinson (I think!).

The rule of thumb I"ve heard is that they can be left alone for their age in months +1. So at 3 months, they can be left for 4 hours. Obviously this depends on the dog and may not be accurate for the first week or so when you get a new dog.

As for exercising, the dog will let you know when they are ready to play. If you can try to have some sort of schedule, that will also help the dog out. The first few days with my pup we walked or played morning, lunch, pre dinner and post dinner. (**disclaimer: she is a HIGH ENERGY dog- either asleep or GO GO GO). For the first few days, she wanted to play all the time as she was anxious and unsure; then she settled in.

I would also recommend setting up a rest area for your dog. We use an exercise pen indoors. I found my new pup was not good at regulating herself and recognizing when she was tired. I learned her 'I'm tired' signals and would put her in her pen and leave her be. Most times she would fall asleep within 5 minutes. If she didn't settle, I would give her a 'calm' toy or chew. Now, she hops in there whenever she is tired or needs a break. But having a space where I could stick her when she or I were tired or needing a break during the day was a sanity-saver.