How can one combine making the most of virtuous times and persisting in good deeds, and what is the criterion for achieving that?

If you find an opportunity for obedience, seize it, and do not abandon worship for fear of slackening, for every worshipper has a period of lassitude after a burst of activity. The intention here is that every worshipper experiences a period of zeal followed by calm and weakness. The guiding principle is not to overdo it or be too hard on yourself, so you don't become averse to worship. Rather, strive to the extent that suits your activity and capacity, without excess. For the one who shows zeal, if he aims correctly and approaches, he is hoped for, and the one pointed to by people with their fingers, do not pass him by. This means that the best deeds are those that are moderate and balanced, and it is not permissible to go to extremes in worship so that it does not become ostentation and seeking reputation. There is no contradiction between the hadith "Seize five things" and "The most beloved deeds are those done consistently, even if small," for both call to seizing life and activity in obedience without excess or severity, and to persisting in deeds, even if small.