Everything starts as Not Available, so you only need to mark the times that could work.
Shortcuts: click a date at the top of a column to fill that entire day. Click a time on the left to fill that hour across the whole week.
On a phone: to scroll the page, swipe on the times down the left side rather than on the calendar blocks themselves. You can also pinch to zoom in if the blocks feel small.
Changed your mind? Come back any time before the deadline, redo it, and submit again using the same name. Your latest answer replaces the old one.