Just to chime in, the HOLD parameter sets how long the envelope will stay sustained, as long as the Trig / MIDI Note is held down.

It is relative to the BPM, with a HOLD of 127 being 1 bar (16 steps) long. In other words, 1 step on the sequencer is a HOLD of 8, 4 steps are 32, etc.

If a Note Off is received, OR if the HOLD time has elapsed, the envelope goes into the Decay phase.