What I mean is, the nuclear chain reactions take microseconds for every generation and that is the reason that nuclear weapons exist. Because in nuclear reactors the reaction rate is much slower thus it can be controlled and prevent it from exploding. So my question here is about the speed of matter-antimatter reaction. Just imagine we have a kilogram of antimatter, is the annihilation speed enough to make it usable as a weapon ?
There exists an antimatter bomb question on this site so i will only address the "speed of reaction" part of the question.
Strong interactions have a characteristic time of strong interactions take place very fast, of order 10^-24 seconds.
Fission and fusion reactions are due to higher order effects between nuclei and in addition depend on lifetimes of individual nuclear levels. An energy transport equation will also modify times to reach your microsecond claim.
A mass of antimatter meeting a mass of matter, at the interface will react within 10^-24 seconds, but again depending on the shape and masses, a transport equation will determine average speed.The neutron 'lifetime' in nuclear chain reaction of 10^-4 second is the start of timing the build up. As a rough estimate of the complicated transport calculation one can expect a faster annihilation of the bomb by at least 10^4, as there will not be a neutron type delay.