I definitely keep going when in the flow! Unless I really need to do something after deep work, I find it’s best to stay in the rhythm of things. 🙂
I believe that it is important to keep your scheduled time and stop when the time has reached the end. I believe so because if you keep working you will feel like you did more and the next time comes if you are tired you msy say "well I did more yesterday " and that is bad for keeping your goal. If you feel like continuing but your scheduled time has finished use that feeling to feel content for you have done a good job and use it also as an opportunity . Think" this feels good…I will do it again tomorrow. "
The recommended time is for me just a must. If you ask me, every additional minutes (or if you're advanced hours) you spend in deep work is better. So just go with the flow, and you'll see in your results that how much more effective you were than before.
It depends on if I have other things to do. Sometimes I'm able to continue working as long as I'm in the flow but others days I don't have time so I have to end when it rings