I work in an open plan office, and find other’s constant conversations incredibly distracting. I find it much easier to get things done if i put headphones in and listen to music- I don’t usually find this distracting when I’m developing, but I do if I’m trying to absorb information -say, reading a book or article.
If it’s pretty clear how to attack a problem, I don’t usually find it takes too long to get in the zone, but it only lasts about 90 minutes to 2 hours before I need a short break.
If the barrier to entry is higher- say, I’m writing a new module where I have to think a bit a about the design - it probably takes me a bit longer to really find flow, as there’s a certain frustration in exploring unsatisfactory ideas as you’re playing around with a problem.