When do they assign you a seat on Vueling?

https://www.remotehub.com/services/details/vueling-asturias-telefono-919-46-41-10-66a22655edae3a0008161eee

Depending on your booking type, random allocation will be available between 7 days and 24 hours before your flight . In the event that there are no random seats available, they will be allocated to you free of charge at the check-in counter on the day of your flight.