I started a new Qtractor session and recorded the melody to “Twinkle, Twinkle Little Star” (playing along to the metronome this time).
I didn’t start playing until bar 9 and so wanted to delete seven bars (leaving one empty bar at the beginning). I tried positioning the playhead (the red vertical line) at the start of bar 8 but was having trouble getting it in exactly the right place. I realized that the Qtractor time counter was set for time (i.e., hours/minutes/seconds) instead of bars and beats.
To change that, I right-clicked in the time counter to the right of the transport buttons. It was set to Time.
I was then able to position the playhead exactly at the start of bar 8. I did this by Shift-clicking the “ruler” above the tracks. Control-click works as well, as does typing the desired position into the time counter.
With the playhead positioned at the desired split point, I right-clicked on the track clip and selected Clip > Split. This split the track into two clips. I then selected the first clip (the empty eight bars at the beginning) and pressed Delete to delete it. I then selected the remaining clip and moved it all the way to the left, so that the first note occurred at the beginning of bar 2.