Excluding weekend hours from time

Afternoon folks

I have a table of data from work "Data Table" (cutting patterns used in a sawmill) and certain patterns have very long running hours due to error reports. The pattern has been "loaded" over the weekend and thinks it has run for several days, in reality it has only run a few hours driving the "m3/hour" right down

The sawmill stops running production every Friday at 3pm and start back up on Monday morning at 6am however it has done overtime on following

Saturday 19/07/2014 06:00 - 14:00 8 hours
Saturday 02/08/2014 06:00 - 14:00 8 hours
Saturday 09/08/2014 06:00 - 14:00 8 hours
Saturday 16/08/2014 06:00 - 14:00 8 hours
Saturday 23/08/2014 06:00 - 14:00 8 hours

Is it possible to remove all hours between the Fri 3pm to Monday 6am except for the times above from all patterns to get a true m3/hour value for each pattern by replacing the hours and minutes columns in the table with some sort of code to do this calculation?

I have attached my sheet for anyone who wants to help

Thanks in advance

Jonny