802.11a preamble

[sdrb <sdrb@xxxxxxx>]

Hello,

I'm reading 802.11a specs and trying to understand how long in 
microseconds is the 802.11a preamble.

I know that 802.11a preamble is 12 symbols long plus one symbol for 
SIGNAL. But how can I convert it to time?

I need to know how many data (counted in time) are added to 802.11 frame 
to be ready to transmit by hardware.