First thing then, if this is a tendency in you, before you sit down, is to decide one meditation subject and keep to it. Because if you start reflections and you're still indecisive, yes it can stretch out longer and longer as you hesitate and hesitate. If you're in normal life and you haven't seen an obvious mental state during the day that gives you a hint of what would be helpful for you to do at that particular time, you could do what one of our assistants did. Make a list of all the different subjects, the reflections we have, cut the list up and put them in a jar. Then just pull one out and see whether you have actually done that recently.
Being a little bit more aware during the day can often help us to figure out what needs to be done. So reviewing the day and seeing some of the difficulties, the cause and effect things that happened during the day helps us to become more aware of what is necessary. The Five Reflections and Compassion/Lovingkindness are very helpful for the basic practice if you find you haven't got an idea of what to do. At least then you can be clearer that whatever you're going to do is going to be beneficial. If you are really indecisive it may mean that you actually have doubt in the mind, so it's helpful to practice some Sympathetic Joy to get some inspiration.
This is why we have a basic practice that we refer back to, and then we have all these other reflections that are often just variants of these basic reflections. If you have a lot of future thoughts arising, then it's a good to do death reflection. So actually making a list is very helpful and making a review of them and asking yourself, "Well, what do I think this reflection is helpful for in balancing, what tendency do I think it is useful for to balance in the practice. What does it help to develop in the practice?" So you can gain a better understanding of the medicine, so you can make an appropriate diagnosis. As we understand the reflections and how they affect the mind, we may become more aware of what is needed, and what reflection is needed, i.e. cause and effect. A lot of the reflections affect us in different ways. Becoming more aware of how they affect us and what is needed is part of wisdom development.
So it appears because you don't really know, it could be helpful to perhaps go through the whole list of the reflections and ask some of these questions of yourself so that you understand more about the medicine and what is useful to be done.