Use the DATEDIFF to return value in milliseconds, seconds, minutes, hours, ...
DATEDIFF(interval, date1, date2)
interval REQUIRED - The time/date part to return. Can be one of the following values:
year, yyyy, yy = Year
quarter, qq, q = Quarter
month, mm, m = month
dayofyear = Day of the year
day, dy, y = Day
week, ww, wk = Week
weekday, dw, w = Weekday
hour, hh = hour
minute, mi, n = Minute
second, ss, s = Second
millisecond, ms = Millisecond
date1, date2 REQUIRED - The two dates to calculate the difference between