Datepickers in mobile app – Is OK required?

I'm going to design a datepicker popup (for a single date). It is going to be like typical calendars, appearing in a box, grouping weeks in rows. Lowest offers are going to be displayed under each day.

So I'm wondering, is it a good idea to place a OK button, and make the date selection a two step task (selecting a day and then pressing OK) or just accepting the date on tapping the day?

At first the one tap alternative seems to be better because of requiring less movements, but in material design and typical controls in iOS, the date picking is a two step task, so I suspect that there must be some rational behind this that I cannot see.

Do you have any idea?