Good idea to start later from SJPDP?

I'm planning to walk the Francés from SJPDP in mid may. I arrive at SJPDP 10am off the overnight sleeper from paris (starting my travels about 6pm the night before from london). I'm wondering if it's advisable to start walking straight away or if I should plan a rest day.

I've walked a shorter camino route before and knowing myself I'll be tired but excited & will want to start walking right off the train. so I'd like to pre-book an albergue for that night and be talked out of it now if it's a terrible idea.

• Will I have enough time to walk to roncesvalles and do the albergue routine (dinner and washing) if I only started about 11am (arr 5-8pm)?
• should I take the lower route instead or stop at Orisson?
• where can I get a stamp in SJPDP at 10-11am?