Question : How can sati arise fast enough in order to be aware of the present moment?
Answer : There is no method which can be followed, but at this moment realities are appearing already. One can begin to develop by understanding of them. If one first listens to the Dhamma and understands what one hears, sati can arise and be aware of the realities. However, we have to listen again and again in order to gain more understanding of realities as non-self. Listening conditions the accumulation of sati and panna, and thus, awareness of the reality which appears can arise and at that moment understanding of it can develop. This is in fact satipatthana. Satipatthana is not a particular method which should be followed in order to be aware of realities. Satipatthana is the development of the understanding of the characteristics of realities which arise and appear, each because of their own conditons.
Do you know ahead of time when realities such as hearing, anger or sati will arise? If there are not the right conditions for hearing we can not cause its arising. Only when there are conditions for it, it arises. Even so, when there are not the right conditions for the arising of sati, we can not cause its arising. When there are the right conditions for sati, it arises and then we will know that there is no self who can cause its arising.
The development of satipatthana is very subtle; if there is no right understanding of its development people will cling to wrong practice. Only panna can eradicate wrong practice. When someone does not know the difference between the moment when there is sati and the moment when there is no sati, he may try to follow another way which is wrong practice. Right understanding of the way how to develop satipatthana is indispensible; panna should know that sati is anatta, non-self, and it should know when there is sati and when there is forgetfulness of realities. If the difference between such moments is not known panna cannot be developed. There will be clinging to the concept of self who tries to "do" something.