It appears that the flash sequences in Airbus and Boeings are different. For example, the following image gives the flashing sequence in Airbus A320:
Image from LED Anticollision Lighting system for A320 by UTC Aerospace Systems
Note the differing flashing sequences of different lights. Also, see this question.
As far as regulations are concerned, 14 CFR 23.1401 - Anticollision light system states that:
(c) Flashing characteristics. The arrangement of the system, that is, the number of light sources, beam width, speed of rotation, and other characteristics, must give an effective flash frequency of not less than 40, nor more than 100, cycles per minute. The effective flash frequency is the frequency at which the airplane's complete anticollision light system is observed from a distance, and applies to each sector of light including any overlaps that exist when the system consists of more than one light source. In overlaps, flash frequencies may exceed 100, but not 180, cycles per minute.