In my experience wrinkly sides, absent a splitting top are indicators that they need a drink. From the angle in the image the tops don’t appear to be splitting which would be an indicator of beginning stages of making new leaves. The outward appearance anyway.

Thank you for your response Stewart. I did give them a little drink yesterday, and the tops were completely closed yesterday. Today the tops suddenly popped open, and I can see little replacement leaves inside. Does this mean I stop watering?

To be honest when mine have split I have never fully stopped watering. They only time I reduce or stop watering is for periods of time in the Winter. But even then not a 100% stop. Just cut way back and give a little drink on a warm day early in the day.

That’s probably completely wrong growing practice but it seems to work for me.

Others my do something different.