Time between timestamps excluding certain hours

Hi. I know this subject has been touched upon a lot in here, but i have failed to make it work for me

Basically, i have two timestamps, I want to find out how many business hours there is between them, so i would be excluding hours between 06:00 and 18:00 from timestamps such as: 08-05-2011 15:32:27 and 09-05-2011 10:10:54 not counting the 12 hours between 6PM and 6AM, but still taking into account that two timestamps can be from the same day but differet times (so just subtracting 12 hours wont work)..

Anyone can point me in the right direction ?

If first stamp in A1 and second in B1,
maybe

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Brilliant, it worked..

Thanks a million :-)

If you have time, could you explain the formula to me ? or point me to where I can read about the functions you use ?

If you have the time..

If nobody else has done it, I'll give it a go tomorrow if you don't mind

Hmm might have been too quick there, it works with the hours but not with the days :-/

As is, It works if one day is, say, 30-08-2011 13:30 and second 31-08-2011 09:00 it counts 7:30 hours which is great, but if i change the first date to 29-08-2011 13:30 it still only counts 7:30 .. I need it to also count the full work hours of the day in between..

Any ideas ??

@Daddylonglegs

Timestamps are always within business hours, Sat and Sun is not business hours

The NETWORKDAYS worked like a charm, thanks :-)..

One question though:
In the odd event the business hours change, which part of the formula should i look at ?