USB-8451 SPI Basic Timing

[JudgeMental]

Two questions about using the USB-8451 SPI Basic to write.

1.  Can the Data line be set to Idle Low, like the Clock?

2.  Writing 17, 24 bit messages using "NI-845x SPI Write Read.vi" in a For Loop. It there a way to reduce the time between messages? It is averaging about 600us between each write.