Whether travelling north to south, or south to north, planning and preparation is the key. The aim is to be in the right place at the right time, and prepared for what to do on arrival. In both directions, the last safe mooring is well before Yarmouth (Stracey Arms on the Bure and Berney Arms on the Yare). Below these points I always see that everybody wears a lifejacket. From now on the currents are fast, the water deep and the consequences of a mistake can easily be more serious.
Don’t forget that having completed the passage through Yarmouth, you need to reach a safe mooring on the other side. If slack water is half an hour before sunset, that is probably not the day to choose unless you have navigation lights and are happy navigating in the dark..