Hi Damian, simply explained, the smaller the latency the faster the memory.

Described in more detail:

Column Address Strobe Latency (CL or CAS Latency for short), also called memory latency, is the time required to address a column in the main memory of a computer. The measure of this is the required number of clock cycles, whereby a lower number is better.

LG

Memory speed (the number of times information is accessed per second) is expressed in MHz. The CAS is the time required to open the information. The aim is to maximise speed while minimising CAS. In your case, between 30 and 32, the difference will be imperceptible.