The POSIX.xs is in the main perl source code distribution. Here's the code for times():

void
times()
    PPCODE:
    struct tms tms;
    clock_t realtime;
    realtime = times( &tms );
    EXTEND(SP,5);
    PUSHs( sv_2mortal( newSViv( (IV) realtime ) ) );
    PUSHs( sv_2mortal( newSViv( (IV) tms.tms_utime ) ) );
    PUSHs( sv_2mortal( newSViv( (IV) tms.tms_stime ) ) );
    PUSHs( sv_2mortal( newSViv( (IV) tms.tms_cutime ) ) );
    PUSHs( sv_2mortal( newSViv( (IV) tms.tms_cstime ) ) );
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It's hard to see how that could cause problems or take much time to return.