Sitting as long as you feel like is not beneficial, because most of the actual work will happen when you start to notice your agitation and at that point is when you will just want to get off the cushion. Stick through it, and watch that agitation and your monkey mind go crazy, until the end of the timer.
I recommend starting with a short timer, 10 minutes, then slowly increase the time.
On another note, I have spent a good deal self-reflecting more or less alone in the dark with me and my thoughts. From what I understand on some parts of the web, this pretty much equates to ”meditation”. While others describe it differently.
I guess I could download HeadSpace and be more explicit about it, but I do anyway think I have derived some mental benefits from the above behavior. Like, being more comfortable with myself. But I don’t think I am doing meditation since I don’t get all benefits as actual meditators.
Just as a reference to the OP of this thread, about being able to distinguish oneself from the voices in one’s head... I think there are more benefits in meditation.
Two phrases that have been very relevant to my practice:
"Being lost in thought is the opposite of concentration."
"Lost in thought is not meditation."
The above is not meant to imply that there aren't benefits to spending time lost in thought.
[1] https://www.amazon.co.uk/Yoga-Consciousness-Practices-Enligh...
I would say sit as long as you feel like it, except that doesn't really help initially. Maybe put on a non-intrusive background track that fades out when time is up? And do take your time when coming back; start by listening, then opening the eyes slowly etc.
Same goes for waking up from regular sleep, but refusing alarms in this society is a pretty serious compromise.