What do the 'startDate' and 'endDate' parameters for createOffering represent?

The start date is the date that your offering accepts investments. The end date is the date that your offering stops accepting investments.

The start date is the date that your offering accepts investments. The end date is the date that your offering stops accepting investments. It is important to note that these dates are not validated against any other method that would cause the method to fail. This means that trades can be created outside these dates without error.