I was a bit concerned about the cut-over from the old database on Heroku, really wanted to minimise downtime. So they helped me produce a step by step plan, test as much of it as possible, then had an engineer join me on Zoom while I made the switchover. They were even able to accomodate doing it in the early morning in my timezone to minimise the impact. Ended up with maybe 5 mins of downtime which I was very happy with.