Let user define the interval they want to get the newletter

Simplenews itself is about sending single newsletters.
It is not about creating automatically creating aggregated content.

So, define the newsletter lists in the way you like (e.g. name them "weekly" and "monthly" and provide appropriate content.

You as administrator decide the moment and the content to send to all recipients.

Note there is a scheduler that allows to send newsletter issue copies on a periodical basis and possibly other interesting modules for things youlike.
For aggreagted autocreated newsletters, check also notifications module.

Simplenews only handled manually triggered newsletters.
For sheduling, look at Simplenews Scheduler, for example, or implement your own solution based on hook_cron().

Well... Simplenews does send a node, so... admitting you're scheduling a newsletter... what would you send ? The last node tagged with the newsletter term ? Any node created between the two mass-mailings ? There doesn't seem to be a rule applicable every time, so you will have to build this functionnality, the module does not provide it.