How to 'tighten' memory timings?

[Modjo]

Hello all. This has been bugging me for a while now as this is the only thing that I haven't been able to suss out. I'm not sure how 'loose' my memory timings are but would like to know (in Laymans terms that is) what it means, does and how to tighten them (if I can).
Here's my settings atm



Thanks in advance