I’m a writer. I can write with concentration about 20 minutes. Any tricks to extend that time to an hour a day?

Cris C.
If you take short breaks in between it may help. I'd say also working your way up, one week start doing 25 minutes. Once you've mastered that move on to 30 minutes. Try to challenge yourself once you've been able to be consistent with your set time for your writing session.

Mathilde Y.
The first thing I can tell you is it as a writer I actually write with a partner. we don't have to be in the same room, often we're just in a chat window throwing ideas at each other, but it really helps.

Whenever I've hit my maximum autonomous capacity, I asked myself what else could go wrong in the scene, what could make it more interesting, or what would happen if I threw in a completely different character. Usually trying to find what could make it go wrong open the whole new Avenue of writing fodder. Because you have to explain why it went wrong, how it went wrong, and then deal with the aftermath. That usually should allow you to extend your writing all the way up to an hour.

whether you keep the scene or not doesn't matter at that particular moment : what matters is your writing.

Alwin Y.
Usually when doing deep work i would not pay any attention to the time, i just concentrate and enjoy the work i do. Usually id hit the 1 hour or 40 mins mark without even realizing.. goodluck!