Periodic mailings... how?

[weirdgod]

I prepared 10 mailings, which I would like to send new subscribers to my list periodically... First one immediately after subscription, then the next one 7 days later, the third 14 days later ... and the rest in same order - one every week...

How do i do that?

I found the Action - Send action based mailing - but predefined values are just from few hours to 7 days max.... Is there a way to change/add new to these, or should I use some entirely different mechanism?

thanks,
jaka