Your dance section begins independently of the neighboring couple
In free Waltz, each couple has its own sequence of movements. The couple in front of you may already have danced several turns while you are still standing at the edge. That doesn't put you behind: you don't have to copy their figure or start at the same point in their sequence. The music is shared, but the sequence of figures is not. It would be different with a choreography danced explicitly together, which this guide is not intended for.
Your own starting position is what matters. If you lead, you need a movement whose beginning you can confidently prepare from standing still. If you follow, you need a clear start to the movement, not a guess about what the neighboring couple is doing. A hurried arm impulse is no substitute for this preparation. If the turn gets stuck as a result, this technical explanation can help you understand why a Viennese Waltz turn gets blocked.
A familiar movement is suitable only if your starting position is right. That's why a hesitation change in Slow Waltz is not a random filler for every Waltz tune. Don't choose anything new when starting out. Your first section should be just as reliable as a movement you have already started together in class. It doesn't matter how late in the song you start.

