seq does not record one byte per millisecond or something, it only records events including
delte time. so after the last note off (for example) the recording is done, no matter how long
you let it run during recording.
if you need that for some reason you could help yoourself out with a special event such as
lowest note to function as "end".
i strongly suggest to look into [detonate].
it only looks complicated – in fact it is easier to make a recording/playing tool for midi or
similar stuff with this object.