Mine used to always take the longest when I was away from home when I also couldn't just leave it outside so I recognise your descriptions above except mine were mainly done in hotel car parks in USA at 3am in the morning or some equally ridiculous time between massive high buildings in London.
I put mine on top of the car and occasionally (well twice) the car is driven off with Garmin still atop - one by me once not. It survived both those journeys but not the journey back from London in a bag with rest of my wet running gear.
Nova I think at your stage you can run whatever you can run when you do something a bit faster as you will be improving every week. Just make sure you don't do too much of the faster stuff - one session a week is probably plenty - and keep the rest of your running nice and slow.