Display error message daily Is there a way to display error message daily to the user saying that "Your subscription Expiry in x days". And this message needs to popup each and everyday.

I can use hook_init()(this will run each and every page load), is there any other hook/option available?
hook_init is used, when you want to do something while the request is initialized, 
you could use hook_preprocess_page and there set the message, checking on a custom field you added to your user, storing the date of the last information. If this is not today, then show it and update the field value.