Timing contractions

Okay, so this is going to sound silly.

The gals that did our quick birthing class said to time contractions from the start of one to the start of another. However, when using an app, that doesn’t seem to work. So my midwife said I should be able to time the contractions on the app from the start to end of a contraction to time them... anyone have input or feedback or a favorite app to use to time contractions? As a second time mom I feel like I should know, but my water broke before I had contractions with my first which is why I knew I was headed into labor.