A sending rule sends offers inside the Schedule time you choose in the rule: Morning (08-12), Noon (12-16), Evening (16-20) or Every 10 minutes* (the last one is not available to every account). To see or change it, open Marketing > Offers Manager > Automation and edit the rule.
Full steps: eBay Offers Manager: Tabs, Bulk Offers and Auto Rules (section: How do I create a rule that sends offers?).