You can use the step-sequencer built into n-Track Drums to program the drum sounds used by each measure of the song. You can open the step sequencer clicking in the "Steps" button in the n-Track Drums property page. You can then assign a blank (i.e. no sound) pattern to the measures corresponding to the first 10-15 seconds of the song and then non-silent patterns to subsequent measures.
You can use the n-Track Drums as a plain MIDI synth, create a regular n-Track MIDI track, program the drum notes during the length of the song by editing the MIDI track in the n-Track Piano Roll window, and assign the output of the MIDI track to be sent to the n-Track Drums plugin with the 'Output' drop-down list in the MIDI track properties box that appears double clicking on the MIDI track.
You can create one or more drum patterns in the pattern editing view of the n-Track Drums, then create a MIDI track and send MIDI notes on MIDI Channel 16 to switch between the patterns you created above. In this way you don't have to create a full MIDI track, you can simply trigger the patterns that are easily created inside n-Track Drums
You can switch from the 1st to the 2nd method above by dragging the musical note button in the upper right part of the n-Track Drums steps view into n-Track's timeline window. This will make n-Track create a new MIDI track with the exact patterns that were used in the Drums steps sequencer. You can then set the MIDI track to have n-Track Drums as its output and edit the sequence in the main n-Track Piano Roll window.
n-Track | Create Music 