Hi Oliver,
I can help point you in the right direction on this.
There is no feature out of the box to change the time to a preset time. The function right now is designed to get the current time of the user rounded to the nearest hour.
There is filter you can try to use to modify the output here:
tribe_community_events_form_start_time_selector
That is found in this file:
\the-events-calendar-community-events\template-tags.php
Custom Datepicker
Or you could follow the themer’s guide to move this file:
\the-events-calendar-community-events\views\community\modules\datepickers.php
And replace this function:
tribe_community_events_form_start_time_selector();