What is proper self paced spiritual meditation retreat etiquette?

I’ve never been on a spiritual retreat yet, I know it’s sad, but I was wondering if we had to be in a meditative posture the whole time or if it was proper to lay on the grass face up or face down after doing the group led activities and they let us go on our own. Or should I do walking meditation if Im not in a sitting posture. It’s in the Theravada tradition I believe. Serious answers only. It will be from 9 am until 5pm.