under DOS the
the wall clock time a program had been running was identical to its use
of the CPU, as it was a single-tasking environment.
In the epoch of single-task environments,
in 1988 (before ISO C standard was published),
internal help of Borland's Turbo C for DOS
already claimed that it's the CPU time
that is returned by clock()
But this is Borland, not MS.
I don't have old Microsoft's C compiler's manual
at my disposal to see how clock() was described there.