Feeding my starter so that it will be ready when I need it

I have mature starter that I’ve been using for awhile. I’m planning on baking tomorrow, so I started to prepare the starter by leaving it at room temperature and feeding it every 12 hours yesterday morning. Last night it expanded quickly, and this morning (12 hours later) it had collapsed. I fed it again, and within one hour I can see it expanding already. I need the starter to be ready tomorrow morning. I’m concerned that if this happens again, (expanding quickly and then shrinking sooner than 12 hours) the starter won’t be ready when I need to bake. Can I alter the schedule to every 8 hours or so to insure that the starter is at its peak when I need it?