As a Student, I have limited time to practice. But overall, I have approximately 1.5 hours on the weekends. So should I do 1.5 hours in one sitting or 45 minutes in 2 seatings?
There's some opinion here, but in my experience as both a performer and teacher, it's more-or-less unanimous that smaller practice sessions are more beneficial than one huge practice block.
Of course there's a law of diminishing returns here; although 2 sessions of 45 minutes will typically be more beneficial than one session of 90 minutes, you'll find that 15 sessions of 6 minutes will typically be detrimental to your progress.
With that said, it's up to you to find your sweet spot. Perhaps 2 sessions of 45 minutes is best for you, or perhaps it will be 3 sessions of 30 minutes. That's something that only you can decide.
Having said that, there will be days (and particular tasks) where one large block of 90 minutes may be better. But that's another question you will have to answer yourself.
I'd lean toward shorter and more frequent sessions. But how short depends on you. Ask yourself how long you can really focus and get good work done. If during a 45 minute session you find your mind wandering and looking forward to being done or playing something different, shorten it up a bit. However long you practice, you should be using that time well. And if you're losing focus you might as well take a break and pick it up later rather than wasting the time.
I use 25 minute sessions whether I'm practicing or working. That works well for me but you may have a longer or shorter attention span.
Also many people find they get the best results by sticking to a schedule. Try to practice at the same time(s) each day and in the same place. That place should be dedicated to practice so that when you're in that place you won't be tempted to do something else or let your mind wander. In other words, it helps put you and keep you in practice mode. For me it's just a corner of the room with a chair and music stand. It doesn't have to be fancy.
Even if you can work in 15-20 minutes a day, this would be more beneficial than one or two sessions on the weekends. The effectiveness increases too when, as suggested, it is at the same time, in the same place every day. I strongly suggest taking a look at your schedule to see if you can possibly work in a 20 minute slot each day, perhaps getting up half an hour early to do so.
Again, I don't know your schedule, so I don't know if this is feasible, but it's highly recommended.
I would not recommend going any shorter than 15/20 minutes, as this will not probably be long enough to be effective. And I certainly don't recommend just one practice session a week, no matter how long. Although as a college piano major I regularly practiced for 1-1.5 hours, this was on a daily, rather than weekly, basis.
It's just a matter of what works for you, but to sum up, shorter (but not too short!) daily practices are more effective than longer weekly ones.
I'm adding up to answers here, not because I'm going to have an original answer, but precisely to emphasise, with all the other anwsers, the fact that small daily sessions are more beneficial than large sessions on the week-end.
Not to mention all the times when you'll have something else to do, have a headake or simply not in the mood to pic up the instrument on the WE.
10 to 20 minutes sessions on a daily basis will keep you going for long. You'll be able to see some progresses in you daily practice, which is an awesome reward.
Actually it should be quite the contrary, you should NOT practice on the week-end, so you have spare time for something else, one day off and renewed pleasure when you pic up the instrument!
Practice for as long as you can with complete and total focus. The amount of time this is varies from person to person. I started out with 5-10 minute practice sessions which over the years have evolved to non-stop practice sessions of 10-90 minutes.
The moment your mind starts wandering, stop and take a break until you can practice again with complete concentration.
The brain's a funny thing. It carries on working when you're not. So prolonged practice sessions, for many, tend to overload it with information, which then takes a long time to absorb, with some being discarded, or at least kept on hold for later. Shorter sessions, with absorbing, organising time for your brain in between, usually works best. Having said that, concert pianists will practise for many hours at a time preparing for the next concert. Strange, maybe, that they need to practise far more than us mere beginners!
When you stop concentrating, your brain is telling you it's had enough for a while. Carry on, and it's pretty well pointless, as most of us have already realised!
It depends exactly what you're trying to 'learn'. If it's more of a physical operation - getting a run to play smoothly - then the motor aspect takes over, and you go for as long as physically possible, maybe.
It does come down to personal opinion, which is off-side here, but actually, each person will have an optimum way/length to practice. Even this will vary considerably over time. We cannot find that for you, only give you parameters. Personally, my 'practice' regime could be ten minutes, 5/6 times a day, but with another 'problem' I'd benefit from a 90 min session, and not stop till I was happy with the result.
A more important factor, often, than actual time spent, is frame of mind, tiredness. For some, an early wake up with a refreshed brain in very productive - certainly better than a last 30 mins before bedtime.
Then of course, we have to consider the big question - What is practice itself? Just sitting down with an instrument is a start... but there's lots more. What do you want to achieve in a session? To understand the harmony of a section? To learn something verbatim? To work out tricky fingering? To learn the format of a piece? The list goes on. perhaps for you, a tick list will help. And all this will hinge on how long you take for a session.
So, you're going to have to answer your own question, by experimentation, depending how tenacious you are to a degree.
From my experience and perspective it really depends on what your goal is. I know musicians who are trying hard to become professional entertainers and they practice 8-10 hours a day. Three years ago I decided I wanted to become a better piano player so I started practicing 2 hours per day....nonstop. I find this time goes by very quickly and I have improved dramatically. My time is spent on progressions around the “circle “ some scales then working on perfection of tune after tune. I play solely from fakebooks.