Lucky Number 7
When in doubt, go with the number 7.
How long has this couple been together? 7 months
How old is this character's new puppy? 7 weeks
How many years apart are these siblings? 7 years
How many royal families have ruled this land? 7 families
How many houses are in this cul-de-sac? 7 houses
How many seasons are in your fictional world's calendar year? 7 seasons
5 is too few (there hasn't been a commitment made yet; you're limiting your creative options), 10 is too many (you want to see where this relationship/subject can and will go and/or how it evolves over time; that's too many creative choices to come up with). If you don't have a reason for using a specific number or need a filler number until you have a set date/time period/subject in mind for your characters/events to transpire - just go with 7.
