Add a second notification to your live wallpapers. Set one for "On Demand" and the other for "Recurring". For the "Recurring" ads, set that schedule to once a day, or once every three days (whatever you want, just don't over-spam your users). As for the time when your users receive the ads, that's irrelevant, set it to whatever you want. In my opinion, 5 minutes is fine.
Stollo when you say add a second notification,do you mean to add the same ad unit notification on my live wallpaper....as for the time when the users get the notification,I set it after 3 hours,Im using this method for 3 days and it is very early to say,but It is working pretty well.
I covered this topic in super detail in another thread: http://www.livewallpapercreator.com/community/index.php?threads/how-to-get-higher-ecpms.240/ And btw, ECPM's of over $2.00 is unrealistic. $1.00-$1.90 is the norm.
No I mean adding another line of code into your live wallpaper to allow for two simultaneous notifications. You can add multiple notifications to the same app in the Leadbolt app dashboard and it will give you different app ID codes. Add a second notification into your live wallpaper that uses that different code so you can control each notification individually. Then set one for "On Demand" and the other for "Recurring". For "Recurring" I recommend once every three days, but you can do whatever. Just don't send more than one per day.