Reading the diagrams on a datasheet is an art
Keep in mind that the diagram itself can be misleading if taken literally. In the real world, the "width" of the various features on the diagram depends on a number of variables, including the clock/bus access speed of the system. Which in the ZX81 are more complex than normal Z80 systems due to the way that the ULA and the Z80 work to generate the data stream for the video.
Okay, the site that I am going to link to is for the 6502, but keep calm, and do have a look, as it does make the timing diagrams make a little more sense. Here's the
link.
Back to the Z80 and 32k byte SRAM chips. Most of these all work the same. After all, they were (mostly) all being used for the same function.
Mark