Horseback Riding for a Beginner?

I am going up to Yosemite National Park in 10 days and I was wondering if a 2 hour horseback ride on a trail would be too long for someone who never rode a horse before. Will my bottom be way too sore? There is a 1 hour option but I am thinking it might be too short. Does anyone have experience with this and should I take the 1 hour ride due to this being my first time and due to soreness?