Possible Clues:

• Call to action
• "It's go time!"
• "Time to go," and a phrase that could be uttered by a 15-, a 21-, a 32-, or a 48-Across?
• 'Time to hit the road!'
• "Time to get the show on the road!"
• "Time to blow this popsicle stand"
• 'Time to get started'