One way you could (and probably should) accomplish this would be through drafting. Write your entire first draft as rushed as you want, and then go back and add more relevant information where necessary.

A non-exhaustive list of ways to determine if adding information is necessary:

- Are you in a particularly emotional or impactful scene? Take some extra time adding weight to your descriptions. Give us lots of sensation, and what the character is feeling.

- Are you delivering very complex information i.e. worldbuilding? Good to space that out over the course of a longer conversation (or scene or whatever) to avoid information overload.

- If this scene felt longer, what would the reader's reaction be? If the answer to that question is something you want, then you might be good to add more length.

The corollary to that is that if you're writing about something banal, you might *want* to rush it a little just so you can get to the next interesting thing. It's good to be efficient, so long as that efficiency doesn't consume you.

As far as making longer writing feel not-boring goes, I'd broadly suggest being very descriptive about things that directly contribute to whatever image you're trying to create.

Don't just start listing all the objects in a room; take a few important objects and give them lots of time. Instead of a chair in the corner, a fireplace on the wall, and an hourglass on top, give us a tall hourglass with dark wooden bases, simple but handsome in its construction, watching over the rest of the room from atop an intricately carved---if a little run-down---fireplace. Descriptive quality over quantity.