Whatever be the time you devote to Japa and meditation - even if it be only ten or fifteen minutes - do it with all your heart and soul. The Lord is the Indweller, the Inner Guide. He sees your heart; His measure is not how long you meditate on Him nor how many times you do Japa, but by your inner longing.
In the beginning Japa and meditation taste rather dry. Yet you must go on practising them, even if it be like swallowing medicine. You will find joy after you have practised steadfastly for three or four years. Then, if you miss your meditation even for one day, you will feel miserable - out of joint, as it were.