This based on a highly simplified idea of how focus works. My experience is that motivation is a far more important factor for me. I struggle a lot with procrastination when my internal motivation is low. Meetings do drain me, but short interuptions are not a problem if I am motivated, but if I am not motivated a cycle of procastination will kick in and it can take me hours from becoming focused again. I often feel ashamed of my procrastination, which makes it harder to get out of it. This is why I do not like fixed working hours. Sometimes, I can focus beter at night than during standard working hours. The break through ideas for fixing problems (hard bugs) often come at random moments when I am not focused on them at all, often during boring daily cores.