For drum synthesizer sounds, the note length is usually irrelevant. It is a rare case where the player may omit the Note OFF events (depending on the synth). For melodic synthesized sounds, you need to apply the musical articulation
rules. When playing legato
you need to match the end time of one note with the start time of the next. When playing staccato
the effective length of the note is a fraction of its nominal length.
See also this old discussion about playing legato with Fluidsynth: