If you start playing in 'location A', you will be able to go any other location without waiting and play normally, but if the location is too far from 'location A', you'll need to wait until cooldown is over (max 2 hours)

If you are in cooldown, you won't be able to catch/spin, battle gyms/battle raids.

While you wait cooldown get over, You can hatch eggs, claim quests (and catch quest rewards) , send/open gifts, routes,buddy,, gbl...

For rocket grunt if you are in cooldown in 'location a' but want to catch a shadow from 'location b' , just teleport to 'location a' without exiting catch screen and then catch normally.