Buen Camino! 18 days is fine but enjoy every one of them. You will be passing some beautiful scenery, do peek into every church, admire the architecture - the art, have fun in Pamplona, seek out the special and the unusal - the Church of Saint Mary of Eunate for example, walk over the medieval bridge at Puente La Reina - walk back and around to see it properly from the bridge over the main road, don't expect much but take a sip of the wine from the Irache wine fountain - even if it's only 0730(!), visit Caesar Borgia at Iglesia de Santa María de Viana, enjoy tapas in Logroño, in short forget kilometers and make the most of everything the Camino can offer.