My Phoenix ROM BIOS PLUS 3.10 didn't reset carry flag when it was
tested reading time.
The lines from D.Rifkind's source code I've modified as below:

*** original ATCLOCK.SYS
                mov     ah, 2h
                stc
                int     1Ah
                jnc     clk_initialize_1

*** modified ATCLOCK.BIN
                mov     ah, 2h
;                stc
                int     1Ah
                cmp     ah, 0
                jz      clk_initialize_1

***

Vincent