I personally would love to see a Time type but it'd be hard to justify.
I imagine it as something typically associated with those that have a mastery over the make up of the universe to such a degree that they can either control, travel through, measure or manipulate time. As such it would be typically associated with legendaries but not exclusive to them, and very rare.
>Super Effective against Ice, Steel, Grass
>Resisted by Ghost, Dragon
>Weak to Dragon, Dark, Poison
>Resists Fire, Fairy
Retconned typings
- Dialga (Dragon/Time)
- Celebi (Grass/Time)
- Klink line (Steel/Time, because it's clockwork)
- Unown (pure Time)
A new cover legendary that would be story relevant in Sword/Shield, a Groundhog that creates time loops to protect things it cares about from danger, which would be what you need to escape in SS.
Moves/abilities associated with Time would have a big focus on impacting turn order.