I have mentioned before my attempts at structuring my days. I have a tendency to get involved in something and just keep going indefinitely (on one hand) or to just never get started (on the other). For this reason creating a structure is important - even though I feel free to modify it on the fly. A long time ago I heard a rule of thumb for ministry that divided the day into morning, afternoon and evening and said that one should work two out of three sessions. This takes into account the fact that so much ministry stuff happens in the evenings. I also need to put in study time so I have divided the day into mornings (three hours plus two hours), afternoons (three hours) and evenings (two hours). Every day I must work for five hours on ministry and three hours on studies. And then take time out!! Because I am busy nearly every evening that works out to three hours ministry and three hours study during the day - so far that is working. Yesterday I did admin at home and worked 7am to 10am. Then I went out without feeling (much) guilt and was back to do study stuff from 1.30 to 4.30 and then meet with someone in the evening.
This sort of loose structure works well for me!