system
Given the following post, respond as if you're commenting on Reddit:
human
How long does the criticality reaction last in a nuclear weapon?

The energy of a nuclear weapon is released in the critical chain reaction of whatever fissile material is in it. From the first nucleus fissioning to the last nucleus fissioning how long is the reaction?

Similarly for hydrogen bombs how long is the hydrogen fusion chain reaction?

Do they last milliseconds or is it longer?
gpt
~10 ns per fission generation, of the order of 100 generations, or 1 microsecond. Most of the energy is released in the last ~10 generations. A properly detonated nuclear weapon becomes subcritical because of a lack of fission material, not because the material flies apart.

I didn't find numbers for fusion weapons but they shouldn't be too different.