In order to serve as PIC of an aircraft, you must have a logbook entry from an authorized instructor certifying you satisfactorily accomplished a FAR 61.56 Flight Review in an aircraft for which you are rated within the preceding 24 calendar months, unless you fall in one of the exceptions. The exceptions include, among other things, passing a pilot proficiency check or practical test conducted by an examiner for a pilot or a flight instructor certificate. The flight review consists of a ground and a flight portion, each for at least 1 hour. It often works out that both portions are completed on the same day by the same flight instructor. But, it is permissible for the ground portion to be conducted by one instructor and the flight portion be conducted by another, and on different days. Remember, though, if done on different days, the first date must be used for calculating the next 24 months of currency.
