You are right: calculate the wait time by subtracting the 2 times and you won't loose any second in precision as system times are in seconds.I could make a calculation by entering the time at which the trigger must fire and then read current time and extrapolate the wait time... But I think it will lack precision .
it will be accurate, but this will only work if he wants the wait time to be 24 hours or less thouh (or 12 hours or less, if using 12 hour clockYou are right: calculate the wait time by subtracting the 2 times and you won't loose any second in precision as system times are in seconds.