This isn't possible as far as I know without writing a large chunk of VBA which would enumerate all messages and their sent date and then convert the date to a day and return a list of emails which matched saturay.
The closest you can probably get is to use advanced find (ctrl+Shift+F), go to the advanced tab and start creating rules for each saturday you want to search.
If you do decide to go down the VBA route, please post whatever code you manage and we will try to help where we can.