An extra few hours from orientation or few days earlier start date aren't going to make a difference one way or the other. Just be honest and you'll be fine.
No it doesn’t. But the date (time started) will make a difference. For example, some of the volunteering positions I have taken take about 2 months the complete the paperwork/background checks/orientation.
I wouldnt count paperwork or background checks. You putting your start date as the first day of your orientation shouldn’t be an issue. My old job actually did this for me.