Is the 2 day Parco Archeologico Del Colosseo pass good for 48 hours from first use?

I will be in Rome for 2 1/2 days and am trying to plan my visits. If I am able to purchase a Full Experience ticket from the archeological's website it says it is for 2 days. Does anyone know...is that for 48 hours from the time of first use? Or is it 2 days, so that if I use it on a Sunday afternoon for the first time, it ends Monday evening?