Grass usually needs to be cut at least once per week in the summer unless you get more rain or water your grass more often.
The rain or watering your grass will cause the grass to grow more often and faster so you might need to mow the grass twice per week during heavy rain or when you water your grass.
I usually mow once per week for my lawn which is usually enough but when I get lots of rain then I sometimes need to up my lawn mowing to twice per week at most.
I never let the grass get too tall before cutting it because it makes it harder for the mower to cut and takes a bit longer to cut it.
So cut the grass when it starts to grow and it will be easier to cut the grass and keep the grass looking nice.