Another method adapted from Paul's example
stringFormat("%02d d %02d:%02d:%02d.%02d",
daysBetween({[.]StartTime}, now()),
hoursBetween({[.]StartTime}, now()) % 24,
minutesBetween({[.]StartTime}, now()) % 60,
secondsBetween({[.]StartTime}, now()) % 60,
millisBetween({[.]StartTime}, now()) % 1000
)