Excel 2007 : Time Formula

thats fantastic! thankyou

One problem I found is if I arrive home before 16:00 it shows a negative value which in turn is deducted from the months total, can I have negative values show and caculated as 0?
Now, at the risk of being cheeky (which I can assure you thats not what I want to be ) at the other end of the scale can I adapt this to if I drive before 07:30 but arrive after 07:30, it will only calculate up till 07:30.

Is it possible to explain the formula in simple terms, I find it intresting but dont understand it.

Thanks Again
Alan