Yes. If you are travelling for 3/4 hour and the tide is running at 4 knots, you would use 3 nm as your current vector. You would then also have to adjust your CTS line. If your boat speed is going to be 12 knots and you will be traveling for 3/4 hours, you would measure out 9 nm for your CTS line.
Could this be done for 3/4 hour tides assuming it’s flowing roughly in the same direction?
Yes. If you are travelling for 3/4 hour and the tide is running at 4 knots, you would use 3 nm as your current vector. You would then also have to adjust your CTS line. If your boat speed is going to be 12 knots and you will be traveling for 3/4 hours, you would measure out 9 nm for your CTS line.
What if you have 4 hours but the tide is changing every hour?