Here’s a bit of VB.NET code. The cycle dates on the job show the current billing cycle. If you need to get deeper than that you can get an InvoiceList and get the dates from it.
' Get a customer, or you can get a BusinessPartnerCollection to get all (or active) customers
Dim cust As BusinessPartner = BusinessPartner.GetBusinessPartnerByName("CustomerName")
' Get list of jobs for customer
Dim jobs As StockingLocationList = StockingLocationList.GetJobsites(False,
JobTreeNodeDisplayType.Name, cust.BusinessPartnerID, Guid.Empty)
' Loop through jobs
For Each job As StockingLocationListItem In jobs