I don't have exact numbers for you and I don't know where you could find them, but I can tell you this about corporations listed on U.S. exchanges or otherwise subject to SEC reporting requirements. All companies announce earnings in about a ±5 day window every 3 months. They typically confirm the actual date and time 2-4 weeks beforehand (to allow time for Wall St analysts who cover the Company to schedule around the announcement). Firms never intentionally release earnings early, only if information is leaked will earnings come out ahead of schedule. Rescheduling is rare and typically comes from companies that have had accounting errors, significant operational trouble, or management changes.
For example, Toshiba had delayed its earnings a few times recently due to an accounting scandal. Most recently, Valeant delayed its earnings announcement after its CEO came back from sick leave. But it is rare for mature, stable companies to do this.