If you're disciplined yes, but there are some situations in which you can't save the game, such as whiled a vehicle is moving through an atmosphere (such as while flying a plane or landing a capsule) or while firing engines. It can't save while the current vehicle is experiencing acceleration other than gravity. So you can get stuck In the game during such activities for a little while.
Yes, you can leave the game in almost any state and then pick up where you left off later. The only exception is suborbital flights, but getting to orbit takes 3 to 5 minutes max.
For the first couple hours, you're going to be reverting to launch/construction every five minutes anyway when you mess up and crash or realize you didn't build your rocket correctly to do what you want to do.
I've had a lot of fun watching my poorly designed ship blow up in hilarious ways than I have actually getting to orbit, so I'd say yes, you can def get a long way in a half hour.