Based on the coast guard tide reports, it is a mathematical certainty that, barring unforeseen events, we can hardly be a second off.
9 seconds sound clip from the All Through the Night (1942) movie soundboard.
You can hear this line at 01:31:11.818 in the Blu-ray version of the movie.
Quote context
[...]
- What vessel is he talking about?
- Quiet.
- At this point, the speed increases from 4 to 9 knots.
- And according to our plan, the vessel will reach the minefield at approximately 5:15.
- So the vessel will reach the minefield at 5:21 exactly.
- Steindorff, check the reports. I'll be back in a minute.
- I don't know, but I got an idea that somewheres off there, we'll find the kid.
[...]