In our busy and hectic lives, there is a question that is bound to come up; what if I miss a day doing my novena? Here's a great answer by Dr. Robert Stackpole that you may want to share with your group:
There is a basic Biblical principle to keep in mind that applies to all of our Lord's promises to St. Faustina, or to any other saint of the Church regarding special graces and favors. Simply put: "Man looks on the outward appearance, but the Lord looks on the heart" (I Sam. 16:7; cf. Heb. 4:12). He knows our every good intention, our every natural weakness, and all the circumstances beyond our control that can get in the way of the fulfillment of our devout desires. What matters to Him is not how much of the novena (or litany, or rosary, or how many first Fridays or first Saturdays) we were able to accomplish, but simply the fact that we honestly tried, and the sincere love with which we did what we could. That good intention in itself is precious to Him! As St. Therese, the Little Flower, once said, 'The Lord looks not on the magnitude of the things we do, but on the love with which we do them."
My advice to those who miss a day of a novena is simply to make a special act of adoration of the infinitely generous, merciful, and compassionate God before continuing with the next day of your Novena (for example, you can use the Prayer for Divine Mercy from St. Faustina's Diary entry 1570; "O Greatly Merciful God, Infinite Goodness..." - a wonderful prayer of hope and trust). On the one hand, such a prayer, said with a sincere heart, more than makes up for any negligence involved - if any was involved at all - in the missed novena day. On the other hand, if the novena day was missed through human weakness (tiredness, forgetfulness) or extenuating circumstances, then this prayer extols the compassionate generosity of our Savior, who keeps His promises to us anyway!