Do my speaker cables have to have the same length?
You might have heard to keep cables the same length for optimal sound performance.
That is a myth and not relevant to typical cable runs in a home system.
So do not worry if one cable is 1m (3ft) and the other 3m (10ft), that will have no impact on the sound.
It would be a different scenario if one side is 3m and the other 50m. The measurable resistance in the longer cable would be much higher, but that would also be most likely not audible.
A good amplifier will have no issues compensating for longer cables and an AVR will take care of time alignment.
Please also see: What Speaker Cables Do You Recommend?
