Here is a quote from Dr Lloyd Jones on prayer from Preachers and Preaching pp. 170-171:
Above all – and this I regard as most important of all – always respond to every impulse to pray. The impulse to pray may come when you are reading or when you are battling with a text. I would make an absolute law of this—always obey such an impulse. Where does it come from? It is the work of the Holy Spirit; it is a part of the meaning of, ‘Work out your own salvation with fear and trembling. For it is God which worketh in you both to will and to do of his good pleasure‘ (Phil. 2:12-13)
This often leads to some of the most remarkable experiences of the minister. So never resist, never postpone it, never push it aside because you are busy. Give yourself to it, yield to it; and you will find not only that you have not been wasting time with respect to the matter with which you are dealing, but that actually it has helped you greatly in that respect. You will experience an ease and a facility in understanding what you are reading, in thinking, in ordering matter for a sermon, in writing, in everything, which is quite astonishing. Such a call to prayer must never be regarded as a distraction; always respond to it immediately and thank God if it happens to you frequently.
It specifically related to those in a preaching ministry, However, I believe it is applicable to all of us. Since reading this statement many years ago it is something I have pondered upon from time-to-time. If I could extend his thoughts further, I would say that we should be asking for these times of impulse that we might have a real unction in prayer and real fellowship with our God. And also a reminder here that if we are too busy to pray then we are too busy and need to sort our lives out.
And finally if you are a preacher you must read Preachers and Preaching.