Heroku and node-cron?

Probably they won't work as you expect in 100%. I mean, if cron execution will be scheduled at the time when your server would be offline, then it won't work. Hobby Dynos on Heroku power-up only at HTTP request and shutdown after some period of inactivity, they won't boot because of cron.

Jobs scheduled by node_cron won't run when your free dynos are sleeping.

As an alternative, you can use the Heroku Scheduler add-on to schedule your cron jobs. That will trigger one-off dynos to run your cron jobs. Provided you don't exceed your monthly allowance of free dyno hours, you will be able to run your cron jobs for free.