Researching how to say How long in Spanish, I came across these three versions

1. ¿Cuánto tiempo...?

2. ¿Cuánto tiempo dura...?

3. ¿Cuánto dura...?

In the third case, I assume tiempo is understood. What I don't get is the function of the word dura (hard). Looking up the meaning of dura makes me every more confused.

Researching how to say How long in Spanish, I came across these three versions

1. ¿Cuánto tiempo...?

2. ¿Cuánto tiempo dura...?

3. ¿Cuánto dura...?

In the third case, I assume tiempo is understood. What I don't get is the function of the word dura (hard). Looking up the meaning of dura makes me every more confused.