There's an old canard about how you don't manage time, you manage yourself. There's certainly a grain of truth in that, but it doesn't say how to actually manage yourself. Criticism without construction sucks.
I think it's better to realize that productivity is the product of time and attention. We all know what time is. If you have to keep synchronized with the rest of the world you have twenty-four hours a day. But, most people assume that "attention" is an act of the will. If pay attention, it's because you choose to pay attention. If you're not productive, well, you didn't choose to pay attention. This is false.
Attention is something more organic. At any moment you have it or you don't. You might have a lot of it, you might have none, but it's not a result of your will, at least not in the present moment.
So, the first question isn't "is there enough time?" but "how can I cultivate a sense of attention?" Actually, that's fairly easy. The only hard part is cutting through the just-plain-wrong masochistic bullshit that surrounds the subject. There are two basic things you can do to improve attention: healthy sleep habits and better scheduling.
Sleep. Most people in the developed world suck at it thanks to two cruel inventions: cheap artificial light and the damned alarm clock. The first makes it possible to extend the waking day. The second "fixes" the resulting long day by curtailing sleep. Sleep deprivation impairs memorization, intelligence, judgment, emotional processing, and (of course) attention. The solution is (in my experience) to return to a tropical day/night cycle: 12 hours of "daytime" when you get stuff done and 12 hours of "nighttime" when you turn off the lights, chill out, and slip off to sleep.
12 attentive hours a day beat the pants off of 18 zombie hours. Actually, you get a few of those hours back once you start waking up naturally--with interest, too, since you wake up on just enough of a cortisol high to really be able to put those morning hours to good use.
Scheduling. This doesn't mean what you think it does. You don't have to plan out your whole day. In fact, that's usually counterproductive. Instead, you pay attention to your level of attention. When bored, you switch tasks. You realize that your attention span is usually only 10 to 20 minutes, so you stop within that time to reevaluate if you're really doing something interesting, and if there's something more interesting and valuable to do. This is where "timeboxing" methods such as Pomodoro have their value.
Sometimes you have to do things that suck and are boring and you can't make more interesting. For those tasks, you just attack them in 5 to 10 minute intervals. You accept only doing the minimum required and use every cheap psychological trick on yourself . Whenever possible, you kill these tasks off for good.
The truth is, you don't suck. Having to do sucky things sucks.
Even if you vanquish boring zombie work and use your time much more efficiently, you'll find that still you have "too much to do." That's because of a variation of the Peter Principle: your expectations of what to do with your time will grow until they exceed what you're actually capable of doing with your time.
The solution here is to guard your time jealously Whenever you have a choice, only the very cream of the crop--the most interesting, most creative, and most valuable things--have the right to your time. Merely interesting, creative, and kinda valuable isn't good enough. For example, you might decide to forgo English-language entertainment for Japanese. Rather than extracting 99% of the content of a computer-security article, you'll cut your reading time to a quarter of what is now--and with selectivity and the Pareto principle, you can still be getting something like 80% of the worthwhile content.
"Only when necessary do half-assed things get half-assed time, but always at full-on focus" should be the goal, clearing your time for the things you care about. Your working time is valuable. Your leisure time is valuable. You don't have to worry about working hard enough enough--let the stuff that wants your time prove that it's good enough for your time.
Finally, focus on improvement, not on its results--looking at results either ends up with disappointment that your not as good as you want to be or complacency since you're "good enough." Find a sustainable pace at which to grow and do and stick with it. As Khatzumoto says: "people overestimate what they can do in a day, and underestimate what they can do in a year."
Those are the fundamentals. Things like "prioritization," "delegation," "speed reading," and "supercharged memory" (including SRS) are bonuses. Built on a solid foundation, they're valuable (and worth looking into). Without the foundation, they're only good for selling self-help books.