How does the lifespan of a B-type star compare to that of an O-type star?

Their lifespans are slightly longer than O-types, though still incredibly short.

Both O-type and B-type stars are extremely massive and luminous, leading to very brief main-sequence lives compared to the majority of stars. O-type stars sit at the absolute pinnacle of mass and therefore exhibit the shortest lifespans, sometimes lasting only a few million years. B-type stars follow closely behind; while they are still far more massive and hotter than solar-type stars, their slightly lower mass profile means their core fusion rate is marginally slower than the O-types. This results in a lifespan that is slightly extended relative to O-stars but remains measured in tens of millions of years, far short of billions.