Appendix 3E to Part-FCL
EXPERIENCE
12. The applicant for a CPL(A) shall have completed at least 200 hours of flight time, including at least:
(a)100 hours as PIC, of which 20 hours of cross-country flight as PIC, which shall include a VFR cross-country flight of at least 540 km (300NM), in the course of which full stoop landings at two aerodromes different from the aerodrome of departure shall be made;
No mention of day or night or of doing it in one day. However, the UK CAA is of the opinion that it must be done in one day as they consider that an overnight stop means that it is no longer a single flight, as required by the Regulation. In fact, if you take the Regulation literally, a full stop landing at each aerodrome could, arguably, mean that it is three (or two) flights in any case.