I'd like to search for flights departing either Fri PM or Sat AM, and returning either Sun PM or Mon AM.
In Google Flights, this requires 4 separate searches. Is there another site/tool that allows such a search?
On Matrix Airfare Search you have the option of searching for flexible dates. In my case I was able to search for flights from LHR to FRA leaving Friday and/or day before and coming back Monday on this day only - but you can change that to be the day before/after. You can also specify what time of day (early morning, midday, etc.)