Build Mailchimp/Aweber Like Backend Functionality (We Use Node.JS)

I am building something VERY similar to Mailchimp / Aweber / Active Campaign email auto responder. 1. There is a Restful API app that should be online all the time. 2. Any user can decide that he wants to do an email blast to 10000 of his customers via email (or send a mass sms text). It has to be scheduled tomorrow at 5pm. 3. The user also decides to create a new "auto-sequence". This automatic sequence is configured in a way that every new subscriber should get a welcome email immediately, and then after 2 days an invitation to a local event, and then, after 3 days, the subscriber should get a "final warning" e-mail saying that there are limited seats left for the local event, so everyone should hurry. The current app is built with Node.JS + Postgresql and hosted on Heroku. So I guess what I don't know how to do is how to schedule something to be executed X hours in the future, and how to do a broadcast without clogging the main Restful API app (run two Node.js apps? One for handling REST api requests and another for background jobs?). Anyway, I want some expert in this area to help me out with this and develop this part for me to start with. That is obviously not the whole scope of the project, there is a lot more to it, and I hope you can help me with that too. I actually need somebody for 40 hours a week, but it is ok if you can only commit to 20+.