Select a post for one Day (Like Post of the day)

And how it the "Post of the day" determined? Do you select one at the start of the day or is it the first post made that day?

You can accomplish this by using the today() helper in eloquent.

Post::where('created_at', '>', today())->get();

select one at the start of the day (any random post for one day)

Simple solution

1. Add a new table called post_of_the_day with a column for post_id and a column for date
2. Add a scheduled task that gets a random post and adds it to the table, with todays date
3. Get the post by using the id and date from the post_of_the_day table

You can even get a list of all previous post ids from the table, to ensure that the same one does not come again