The Camino Portugues from Porto typically takes at least 10 days (via the traditional route). You spend the first five days in Portugal, then cross into Spain. Some newer routes, along the coast and the Spiritual Variant can take a couple of days longer. I have not yet walked these, so I cannot speak directly to them.
Don't forget to advance your watch one-hour when you cross the river. Spain is on CET (Paris, Rome, Berlin). Portugal is in the same time zone as London.
In 2015, I started from Porto along the coast, then cut inland at Villa do Conde, towards Rates. The coast was boring to me as I grew up literally on the other side of the same body of water. Everything was identical, except for the sun's position.
As mentioned, at Villa do Conde, I turned to the east to join the internal route. That took 10 days. In 2017, I left Porto on the inland route. This also took 10 days.
On both occasions I used the Metro [2015] (to Matosinhos (next to last stop - climb stairs, cross bridge) or a train [2017] (to near Vilarinho, then walk to Vilarinho) to skip over the industrial areas and city barrios that are difficult to walk through, at least IMHO.
Others have alternative views on this. I respect those differences of opinion.
Personally, I do not like walking where the walking is either tedious or dangerous if I can avoid it. Plus, industrial estates, office parks, light industry or rows of big box stores and outlets do not help my emotional state, so I avoid them. In the Brierely books, these are the areas surrounding larger towns and cities and usually shaded grey.
On the Portuguese route the only area where you need to "suck it up" and endure the 'industrial ambiance' is coming into Porrino. It is within the 100 km limit for being eligible for a Compostela. Cheat here, and you run the risk of not being compliant... just sayin...
NOTE: There are also much smaller industrial belts around Redondela and Pontevedra, but these are not onerous, at least IMHO.
Hope this helps.