No worries. 
If you lower the topics per period in top page number to something that is less than the amount of topics for today it will allow the default to show as ‘daily’:
If it is a higher number than the new topics for today it will flip to the next period that satisfies the topics per period in top page amount:
(I have only created one topic on my test site in the last day)
And I think topics per period in top summary also plays a role for anonymous users as well. 