For a year now, I've been practicing focusing on a single task for about 1 hour a day. After about 6 months, I bumped it up to 1.5 hours, which is where I'm at now.
This usually takes the form of me thinking about what task I'm going to start working on then starting a stopwatch, and I won't stop working until I hit my 1.5 hour goal. On a good day, I'll take a quick break and restart the stopwatch for another round. This gives me 3 hours of completely focused work time, and I'm always surprised by how much I can get done in this relatively short time frame just by forcing myself to focus.
By doing this practice, I realized how much of my so called working time is spent multitasking and distracted. The fact that this focus time is a practice may be evidence enough, but you can imagine checking email, slack and your phone all constitute an interruption in your work, which slow you down and most likely affect the quality of the work you're producing.
In the beginning, it wasn't easy to just sit down for an hour and work on one task. I felt the temptations to take a break, or look at my phone. When I hit a roadblock or was having trouble solving a hard problem, the temptations were even stronger. I'd be tempted to end the mental suffering by taking a quick hit of Instagram. I often did.
Now if I'm working on my computer and I don't know what to do next, or I'm stuck, I just sit there. Usually my brain stops getting ancy after a minute and gets back to work. If I'm really stuck, I start planning on how to get unstuck. If I get writers block, I just force myself to stare at the screen. The point is to build the capacity of focusing and sitting with problems for a duration of your choosing.
I feel like my work quality and speed has taken a leap forward this year. My ability to work around problems and find solutions quickly has improved drastically because of this practice. I think I'll continue it.