Berlin and Frankfurt are in the same time zone. Both cities use Central European Time (CET/CEST). When it's noon in Berlin, it's also noon in Frankfurt.
Both cities observe daylight saving time, switching between CET (UTC+1) in winter and CEST (UTC+2) in summer.
Any time works! Since both cities are in the same time zone, scheduling calls is never a problem. Business hours are identical.
Berlin is Germany's capital while Frankfurt is its financial center and home to the European Central Bank. High-speed ICE trains connect the cities in about 4 hours, while flights take just 1 hour.