I would like 30 days would be more then acceptable if the target is forthcoming in population of the data room and answering inquiries. At most I would expect 60 days if the latter is delayed at any phase.
“A 20M EU revenues, family-owned SME” does not say much about the company. A red-flag due diligence should take a couple of weeks maximum and should be the priority. Once it is done, it is a Buyer Due Diligence, 8 to 12 weeks depending on the quality of the Data Room (if any!).