Sa1lesforce.com has set some limits on Apex Scheduler. Following are the limits in Apex Scheduler in Salesforce.com.

1. You can only have 100 scheduled Apex jobs at one time(Maximum number of Apex classes scheduled concurrently).

2. The maximum number of scheduled Apex executions per a 24-hour period is 250,000 or the number of user licenses in your organization multiplied by 200, whichever is greater. The licenses that count toward this limit are full Salesforce user licenses or Force.com App Subscription user licenses. Chatter Free, Chatter customer users, Customer Portal User, and partner portal User licenses aren’t included.