Order of radio button options and default option

I am currently putting a form together for subscribing to email notifications. One of the options called 'Frequency' allows the user to select how frequently they want to receive notifications. At the moment, we are debating the ordering of the frequency options.

My query is whether or not we should be ordering the four options based on the amount of time (i.e. Every 4 hours, Every 12 hours, Daily, Custom (Custom allows them to select Monday-Sunday which would be displayed in checkboxes below 'Custom' if it is selected only)), or if we should order by most frequently used (daily being the most frequently used option which is why it must be the default option selected).

Note: These options are set in stone, and the default option selected must be 'Daily' (which is the most popular option with our users.

Below are the two options. Feedback would be much appreciated.