To snooze multiple tasks at once, you should select those tasks by pressing cmd/ctrl (Mac and Windows respectively) on your keyboard and clicking on them to add them to your selection. You can also press shift and click two tasks to select them and every task in between them.
Once you've selected tasks, the bulk editing menu will appear at the top. There you will see the "Snooze" button:
After clicking on the "Snooze" button you will be able to either snooze selected tasks for a number of hours or until a certain time: