You need to assume that if you meet for drinks the time will be on the clock unless the provider specifies it.
There might be some providers who might meet you first for a drink to get to know you without being on the clock but many providers expect to be compensated for their time whether it is drinks or BCD.
I have met a gent downstairs for drinks many times but in these situations the gents booked multi-hour appts which would allow enough time for a quick drink first.