Hi,
my quartz is 7,37MHz, which gives 1,6us cycle

No, it is ~3.3us because MOVX takes 24 OSC.
For me it seems that all timings defined for DS12C887 are not critical to be used with your MCU at this frequence. Indeed, you should check it yourself to be sure.
Make a paper copy of timing diagrams of RTC, fill them with pencil according timings which AT89C52 produces at selected frequency (look on its datasheet at figures External Data Memory Read/Write Cycle). Finally, compare values from diagram with those indicated in datasheet of RTC. It is your work, really.

Regards,
Oleg