code to force xls file to open after several hours passed

Hi All

i am tring to write a code to force xls file open by it self when several hours (any number of hours, say 3 hours) has passed..

either pased on a condition Like A1=Now() so when 3 hours paased then, or
based on the computer time so after 3 hours passed then

my try was as follwing (placed in workbook_open) or somewhere else

If A1
getopenfile( file path)
end if

any help is appreciated in advanced