Is there a standard for the frequency/interval between flashes of anti collision strobe light?
For the FAA, this can be found in 14 CFR Part 25 - AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES, Subpart F - Equipment, Lights (§§ 25.1381 - 25.1403):


  § 25.1401 Anticollision light system.
  (a) General. The airplane must have an anticollision light system that -
  
  (1) Consists of one or more approved anticollision lights located so that their light will not impair the crew's vision or detract from the conspicuity of the position lights; and
  
  (2) Meets the requirements of paragraphs (b) through (f) of this section.
  
  ...
  
  (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.


Similar sections can be found for other types of aircraft in other sections; the specified flash rate is identical for all of them.

US military aircraft are not bound by FAA rules, of course, but they tend to voluntarily comply with them anyway unless they have a good reason not to.