Credit to @jwijffels for this great solution:
require(ffbase)
MyData$SalesReportDateYear <- with(MyData["SalesReportDate"], format(SalesReportDate, "%Y"), by = 250000)
MyData$SalesReportDateMonth <- with(MyData["SalesReportDate"], format(SalesReportDate, "%m"), by = 250000)
MyData$SalesReportDateDay <- with(MyData["SalesReportDate"], format(SalesReportDate, "%d"), by = 250000)