Hello,
You are walking this week? The excitement must be overwhelming.
Let's see, you don't mention how far you have traveled before getting to SJPdP. If you are coming from far away, this could be a challenge to start on the same day. For now, I'll assume you will be ready to go as soon as possible.
I don't think you will have to spend much time at the office during this time of year. It is great to arrive, get some information, get passport, check weather report for sure. A 10 minute walk to office, 1/2 hour at office, pick up some food supplies if haven't already, and then on your way.
The first time I walked to Roncesvalles, it took me 6.5 hours with a small break. The second time it took me just a little over 5 hours in a complete freezing rain storm. Not a good picture day, so I simply went at my fun pace and had a blast. I train quite a bit, so this isn't the norm for everyone.
So if you start 10 or half 1o, you could have an amazing first day and still arrive early eve. Dang, I wish I was doing this now.
Don't worry, having no idea is one of the best parts of the Camino. I often see those who have all the ideas and not last more than a couple of days.
One thing we can be certain is to trust the arrows and listen to our bodies. Oops, that's two things.
Keep a smile,
Simeon