Google Calendar integration: How to exclude some hours not to be scheduled?

Following. For sure want that CSS solution you're talking about

This will require form specific custom css code. Please let us know in which form you have added the date picker field with 24 hrs time format, we will sent send you the required custom css code. 

For example:

In this form which I have integrated with google calendar, I have injected the following custom css code to hide the time from 9:00 to 17:00:

#hour_23 > option:nth-child(11), #hour_23 > option:nth-child(12), #hour_23 > option:nth-child(13), #hour_23 > option:nth-child(14), #hour_23 > option:nth-child(15), #hour_23 > option:nth-child(16), #hour_23 > option:nth-child(17), #hour_23 > option:nth-child(18), #hour_23 > option:nth-child(19) {

    display: none !important;

}

Please take a look at the above form and see if this is what you want to achieve.

We will wait for your response.