Going to my first ever MLB game need some help

I’ve lived 12 hours from the nearest stadium my whole life but I’m taking up a job in Vancouver Canada which is only 2 hours from Seattle and so I’m gonna go on April 17th. I was just wondering does anybody know when’s the earliest I’d be allowed in the stadium? I want to catch some BP and hopefully get some baseball cards signed any info would be appreciated. Still can’t believe I’m finally gonna get to see the Astros