Window of opportunity around very active starter

Hi all - pretty newbie SD learner here.

Have messed around for a few weeks now, and managed to keep a starter going.

In the UK, and last week was pretty warm, and my starter overflowed it's jar. So I put it in the fridge and pulled it out yesterday. It was grey with a layer of hooch, but I took 100g and fed it 1:1:1.

A few hours later it had doubled in size and looked very active.

Today it's fallen back down.

My Q is at what stage is it best to use it to bake ? As it's at it's maximum (i.e. yesterday ?). Or will it be OK as is today ? Or should I feed it again and use it when it's visibly active ?

Using regular wholemeal flour.