Firstly the DKZ-B is an American, not a Russian designation. The Russian GRAU index code for the fuze is 9E231 (9Э231). I could not find its general Russian designation when researching the MRV (9E210) fuze family and 9M22 rocket family for the company I work for. A logical one would be MRV-1, as it is a truly minor modification of the MRV.
It looks virtually the same as the MRV, the main change being the colouration of the outer plastic rear portion. It looks similar to the later MRV-U (9E244), but is of a different physical construction and its internal operation is totally different. The only components that are common in function between the 9E231 and the MRV-U are the two-position (short and long) pyrotechnic delay system and the booster.
It was developed by Russia from its MRV fuze for use with the shorter range and slower 9M22M HE-frag rocket that was used by the 9P132 single-tube launcher of the Grad-P Partizan. The fuze, rocket and launcher were rapidly developed by Russian for use by Vietnamese forces opposing US and South Vietnamese Forces in Vietnam. The designation given to the rocket by the US Forces in Vietnam was either DKZ or DKZ-66, hence the DKZ-B fuze designation.
The fuze was cloned by the Chinese, possible designations seen for it being the MJ-4, MJ-4A, and the DRAO-4.
There are detailed descriptions of the MRV, 9E231 and MRV-U written by me on the website of the company I work for.
Sectional diagrams of the MRV, 9E231 and MRV-U.
The MRV...
The 9E231 (DKZ-B)...
And the MRV-U.