http://www.usccb.org/beliefs-and-teachings/how-we-teach/new-evangelization/year-of-faith/how-to-pray-the-chaplet-of-divine-mercy.cfm
The Divine Mercy Chaplet can be prayed at any time of the day/night, but is usually prayed during the Holy Hour of 3:00 p.m., when tradition teaches us that Jesus died. The Divine Mercy Chaplet is prayed on Fridays at 7:30 a.m. (before Mass) at the church of daily Mass. Please see the calendar or current bulletin to find out which church daily Mass is being held at.