As a GENERAL thing, the main starting days of any week from any major starting node, such as: St. Jean Pied de Port, Pamplona, Logrono, Burgos, Leon, Astorga, Ponferrada, O'Cebreiro, Sarria, etc. will be Friday, Saturday and Sunday. The day before a holiday, the holiday proper, and the immediate day after the holiday, are also popular starting days.
Across Europe, most nations still honor the Catholic Holy Days as national holidays and people are off work. Many combine personal holiday time to stretch this further.
For example, around Easter, most European folks have Holy Thursday and Good Friday off, as well as Easter Monday. Thus, someone wanting to walk a stretch of the Camino. could start walking on the Thursday and continue walking for ten days, and only have four days chargeable to personal holiday time.
Personally, when walking the
Camino Frances, I usually leave a week or more AFTER the Easter holiday, to avoid this phenomenon.
The holiday stretch and bridge holidays notwithstanding, I urge people to avoid arriving at a major departure node on a Friday, or Saturday to be able to obtain a bed. Again, and as an example, if you were concerned that there will be a surge of folks leaving from SJPdP on a Friday, Saturday or Sunday, you would plan your arrival by train and departure on Camino so you left St. Jean on a Thursday or a Monday, Tuesday, or Wednesday. In the case of Easter, departing on the Tuesday after Easter would be the earliest I could recommend.
The same "surfing" paradigm holds true all the way down the
Camino Frances. You can reliably presume that there will be a surge or larger wave of pilgrims starting on Friday, Saturday or Sunday from any of the major train and bus-connected places mentioned above.
This creates a concomitant greater demand for bed space of all kinds down the trail. To avoid much of the unpleasantness this entails, at any time of the year, just arrange your travel plans to arrive at St. Jean on a Sunday or Monday, with a Monday or Tuesday departure.
Your goal is to keep the wave of weekend Camino starters either a day or two in front of you, or a day or two behind you. Just remember that you are trying to walk in the trough, or low point, between the larger waves. As you walk West, you may need to schedule a rest day, or a bus skip-ahead over industrial areas, to maintain this pattern of congestion avoidance.
I hope this helps.