Delivery always comes first
No matter what you're doing or how important it is, the delivery will always come first. Did you promise to deliver something until a deadline and you won't make it? Inform your team and your manager so we can create a plan together about new deadlines and plot scenarios. Give room for people to process the information. Don't tell people on the last day.
This principle doesn't mean we need to deliver things at any cost. Other principles must be respected also. If you see that the deadlines are hurting other principles, like doing the things right, talk with the team about it.
It's also important to state that the delivery goal must be clear. Delivering a PoC means that you can do stuff in a more unorganised way once it's not something that will go to production by any means.