That sounds right to me. "Speak now or forever hold your peace" is definitely something we can say to mean "If you need something or you want to say something, say it now because you may not get another chance for a while." My mom used to say it when I was a kid and we were going on a road trip, spending hours at a time in the car. Whenever we stopped to take a break, sometimes I would not need to use the bathroom, so I would not get out of the car. She would say "Do you need to use the bathroom? Speak now or forever hold your peace."