Voltage conversion 3.3v -> 24v

These work nicely for switching higher voltages from FPGA IOs:

http://www.irf.com/product-info/datasheets/data/pvg612.pdf

but they're a little slow for your needs.

Have you though of using a power supply MOSFET driver?

For example, look at page 25 of this schematic:

http://www.ovro.caltech.edu/~dwh/carma_board/gda06rb004_carma_v0.87_dec03.pdf

The Texas Instruments UCC27223 are logic-level input MOSFET drivers. You could use that component, or something similar, to switch 24V pretty rapidly, you'd just need to use MOSFETs with the right voltage rating.

Cheers,

Dave