1,000 workflow time triggers per hour is the current Salesforce limit for time trigger actions.

If you have 1100 time trigger actions to be executed between 7am and 8am, Salesforce executes 1000 between 7am and 8am and remaining 100 after 8am. Once the limit is reached Salesforce defers processing and resumes in the next our.

Salesforce limits the number of total and active rules in your org, the number of time triggers and actions per rule. It also processes a limited number of daily emails and hourly time triggers.

When workflows approach or exceed certain limits, Salesforce sends a warning email to the default workflow user or if the default workflow user isn’t set then to an active system administrator.

HourlyTimeBasedWorkflow from OrgLimits.getAll() can give you the current limit.

Sample Code to find the current limit:

OrgLimit o = OrgLimits.getMap().get( 'HourlyTimeBasedWorkflow' );
System.debug( 'Hourly Time-based Workflow Limit is ' + o.getName() + ' - ' + o.getValue() + ' - ' + o.getLimit() );

Even though the limit is 1000, in my org it was set it to 50. Raise Salesforce support ticket to increase the limit.