Convert calendar date-time to the time difference comparing to the ICU admission time.
deltaTime(record, pseudotime = FALSE, units = "hours", tdiff = FALSE)
ccRecord
logical If pseudotime is set to be TRUE, then the admission and discharge time will be set as the earliest and latest data stamp in the record.
units of delta time, which can be "hours", "mins", "days".
if false the delta time will be written in numeric format.