It was bothering me quite a bit in the past, but I came to a conclusion that "slacking off" is actually a part of work. I wouldn't be able to achieve tasks if I was not able to let my mind wander off a bit and while you could say I am technically not working, I am still being constricted by the task I am supposed to complete and subconsciously thinking about it. For instance, during the working day, often you would see me type something for like half an hour and rest of the day "slacking", but what I type in is well thought through (I hope!) and usually works the first time as intended. Everyone is also happy with pace of my delivery.

Would I be able to do more tasks during the day if I only spent 30 minutes on typing? No. I tried and it is too taxing and leads to burn out. When I was younger I would literally be whizzing through tasks, but by the end of the day, I wouldn't even be able to speak properly. Completely brain dead. It sent me through severe depression and eventually I had to quit the job I had then for my sanity.

Basically if I have a task to do, I bill for it for each working hour (typically 7.5) until it's done.