Well there are two ways you can do this: leave your thermostat on auto and in your ecobee schedule for sleep set the low target tempeture very low like 30 or 20 (lol I am pretty sure you won’t like it colder than that ;)) and don’t touch your thermostat anymore.
In node read you definitely can change the hvac mode of your ecobee from off to auto, cool and etc. You can use big timer, message change, and call service to switch between those modes at specific time. The downside with this method is if you want to change your schedule you have to do it in Node Red.
But overall I can tell you that you can change the hvac mode, I have implemented in my setup and works flawlessly.
I am going to be swampt untill end of the month but if by than you can’t figure it out I am willing to help you set it up specifically for your needs. Just message me to remind me.