to change the start hour (the first that is visible) is easy with just modifying one parameter, however to change the total hours displayed would require some heavier CSS adjustments. The same way, hide Sat and Sun will be tricky... also quite some CSS styling would be necessary for that, I'm afraid.

How can I adjust the first visible?

you need to modify one parameter in the JS file located here: /components/com_calendarplanner/assets/common.js.

in line 4, you will see this:

var vertical_move = 28;

this is the parameter you need to change.

this number must be 4 times the start hour you want. in this case, the start hour is 7am, therefore 7*4 = 28.

let me know if this helps.

Thanks!