Four business days is the recommended number of days between calls when reaching out to contacts at strategic accounts. A strategic account is a high-value account that has a significant impact on the sales rep's revenue, growth, and reputation. Four business days is a reasonable interval that allows the sales rep to maintain communication, engagement, and momentum with the contacts, as well as to avoid being too pushy or annoying. Reference: https://www.salesforce.com/resources/articles/account-management/#account-management-best-practices