How long should it take to write to flash?

Here is the part number that shows up when I use the USB Blaster.

Info: Device 2 CFI Flash 1 is Numonyx JS28F256P33 Bottom Boot (16 bits data bus)

And the settings out of system.h.# define ALT_MODULE_CLASS_cfi_flash altera_avalon_cfi_flash# define CFI_FLASH_HOLD_VALUE 0# define CFI_FLASH_IRQ -1# define CFI_FLASH_IRQ_INTERRUPT_CONTROLLER_ID -1# define CFI_FLASH_NAME "/dev/cfi_flash"# define CFI_FLASH_SETUP_VALUE 80# define CFI_FLASH_SIZE 33554432u# define CFI_FLASH_SPAN 33554432# define CFI_FLASH_TIMING_UNITS "ns"# define CFI_FLASH_TYPE "altera_avalon_cfi_flash"# define CFI_FLASH_WAIT_VALUE 50

The alt_write _flash function appears to compare the memory, erase, then write. If the data to be written is the same as the flash it only takes a fraction of a second, so I assume it only erases and writes the block if necessary.

Is there a formula that I could use to calculate how long a block write should take?