They should be optional, and readers should be able to skip them without being confused when they return to the story.
There will be plenty of readers that will of course want to read everything, but you will also get readers that don't, and you don't want to punish those readers for not reading what can be seen as an 'extra'
That's not saying you can't have improtant or fun information during thses in-betweens, just nothing that will directly interfear with the flow of the story.
Take Prof. Oak at the end of pokemon episodes (not sure if they're still doing this). He'll talk to kids a little bit more about the pokemon featured in the episode, which is fun for the kids that would be interested in that and ads to the lore and factoids for the series, but also leave the series 100% watchable for the kids that don't want to watch that / just don't have the attention span for it.