Hi! I need help with filling in missing time intervals to account for all minutes of the day starting from 12:00 AM to 11:59 PM.  Variables: ID date start_time end_time activity    How do I fill in the missing time intervals with activity="default minutes" to include the end_time of the previous observation and the start_time of the following observation for a whole dataset? For example,   ID date start_time end_time activity 1 03/01/2002 12:00 AM  6:00 AM sleep 1 03/01/2002   6:00 AM  6:30 AM eating 1 03/01/2002   7:30 AM  8:00 AM riding in car  1 03/01/2002   1:00 PM  2:00 PM default minutes 1 03/01/2002   8:00 PM  11:59 PM sleep   I appreciate any help!!!  ... View more